The Morphology and Taxonomic Value of Thoracic Structures in Some Brachycera, Diptera

THE MORPHOLOGY AND TAXONOMIC VALUE OF THORACIC STRUCTURES IN SOME BRACHYCERA, DIPTERA

by MUSA ABDALLA AHMED, D.I.C., M.Sc. (London)

Thesis submitted for the degree of Doctor of Philosophy of the University of London

Department of Pure and Applied Biology, Imperial College of Science and Technology, South Kensington, S.W.7.

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/r? f/ie name o/ God, f/?e Merciful, the Mercy-Giving

He taught Adam all the names of everything; then presented them to the angels, and said: "Tell me the names of these, if you are truthful." They said: "Glory be to You; we have no knowledge except what You have taught us. You are the Aware, the Wise!" He said: "Adam, tell them their names."

Once he had told them their names, He said: "Did I not tell you that I know the Unseen in Heaven and Earth? I know whatever you disclose and whatever you have been hiding."

The Cow 2: 31-33 THE MORPHOLOGY AND TAXONOMIC VALUE OF THORACIC STRUCTURES IN SOME BRACHYCERA, DIPTERA

ABSTRACT

The thoracic morphology of some Brachycera (Diptera) is considered. The results are presented in descriptions of the thoracic skeletons of 19 species from 19 families, together with 76 text figures, and a systematic survey of major families.

Homologies of parts are suggested and a uniform morphological terminology is used for these.

The possible use of some exoskeletal and endoskeletal structures in Brachycera systematics is assessed. Among those features given particular attention are the sella (presternum), posterior intersegmental suture and probasisternum (prosternum) . The Asilids possess a sella which is sufficiently distinct both to unite them as a monophyletic group and to separate them from other Brachycera. The shape of the sella readily divides the Bombyliidae into two major groups, Anthracinae and Bombyliinae sensu lato, thus confirming the broad trad- itional classification of this family. The state of the posterior intersegmental suture can be reliably used for recognition of the Empidoidea as a discrete and natural group. The condition of probasisternum, whether or not united to the proepisternum, helps to define subfamily limits in Empididae,

Some genera have been found to possess a prephragma of a characteristic shape, but these shapes may occur independently in different groups.

Of the peculiar features demonstrated by Systropus edwardsi (Bombyliidae) the following are reported for the first time: the profurcal pits are confluent, the prospina- sternum is present and gives rise to a well developed spina internally, and the metafurca extends in the thoracic cavity as a single, cup-shaped structure. I - iv -

ACKNOWLEDGEMENTS

This study has been conducted under the supervision of Mr. H.E. Goto, to whom I am most grateful for many useful suggestions and. for critically reading the manuscript.

I have been fortunate during the course of my work to benefit from the extensive knowledge and experience of Professor R.G. Davies, especially in matters concerning nomenclature and homologies.

Donation of specimens from the collections of the British Museum (N.H.) has greatly facilitated my work. For this I am indebted to members of staff of the Diptera Section. Special thanks are due to Mr. B. H. Cogan for his never-fading consideration and for selflessly attending to every request for specimens.

I owe a debt of gratitude to Prof essor J. Bowden of Rotham- stead Experimental Station for providing material from his own collection, for his stimulating conversations and for his interest in the project.

The most generous gifts of specimens came from the private collections of Dr. J. Wilcox of Anaheim, California and Mr. C. E. Dyte of Slough Laboratory, to both of whom I am extremely grateful.

I also appreciate the help of those who have sent me specimens and/or literature. They are: Dr. H. Ulrich, Museum Alexander Koenig, Bonn; Dr. D. W. Webb, Illinois Institute of Natural Resources, Champaign; Dr. W. W. Worth, U.S. National Museum, Washington; Professor L. L. Pechuman, Department of Entomology, Cornell University, Ithaca; Dr. R. Matsuda and Dr. H. J. Teskey, Biosystematics Institute, Ottawa; Dr. J. Waage, Imperial College Field Station; Dr. J. G. Londt, Natal Museum; Mr. M. A. Cotton, R.C.S. London,; and the late Osman H. Adlan, Agricultural Research - V -

Corporation, Wad Medani, Sudan.

I acknowledge Elizabeth Jenks for her patience in typing the thesis.

Thanks to the authorities of the Agricultural Research Corporation, Wad Medani, Sudan, for financial support. - vi

LIST OF FIGURES FiPage 1. Lateral view of the thorax of Atylotus agrestis with details of sutures 78

2. Lateral view of the thorax of A. agrestis with details of sclerites 79

3. Lateral internal view of the thorax of A. agrestis 80

4. Sternum of A. agrestis 81 a. ventral view b. dorsal internal view

5. Ventral view of the probasisternum in Tabanidae 82 a. Haematopota patellicornis b. Chrysops brucei

6. a. Posterior internal view of the prephragma of 83 A. agrestis b. Posterior internal view of the metafurca of A. agrestis

7. Lateral view of the thorax of Pelecorhynchus fusconiger

8. Lateral view of the thorax of Pantophthalmus tabaninus 85

9. a. Ventral view of the probasisternum of 86 Pelecorhynchus fusconiger b. Ventral view of the probasisternum of Pantophthalmus tabaninus

10. Posterior internal view of the prephragma 87 a. Pelecorhynchus fusconiger b. Pantophthalmus tabaninus

11. Lateral view of the thorax of Chorisops tibialis 88

12. Lateral internal view of the thorax of C. tibialis 89 - vii -

Fig. Page 13. Sternum of C. tibialis 90 a. ventral view b. dorsal internal view 14. Ventral view of the probasisternum in Stratiomyidae 91 a. Beris chalybeata b. Merosargus stamineus

15. Ventral view of the probasisternum in Stratiomyidae 92 a. Stratiomys chamaeleon b. Hermetia illucens 16. Posterior internal view of the prephragma in Stratiomyidae 93 a. Chorisops tibialis b. Pachygaster atra 17. Posterior internal view of the prephragma in Stratiomyidae 9A a. Hermetia illucens b. Merosargus stamineus 18. a. Lateral view of the thorax of Xylomya tenthredinoides 95 b. Lateral view of the thorax of Xylophagus fulgidus

19. Ventral view of the probasisternum 96 a. Xylophagus fulgidus b. Xylomya tenthredinoides 20. Posterior internal view of the prephragma 97 a. Xylophagus fulgidus b. Xylomya tenthredinoides 21. Lateral view of the thorax of Coenomyia ferruginea 98 a. external b. internal 22. a. Posterior internal view of the prephragma of ' Fekruginea 99 b. Ventral view of the probasisternum of C. ferruginea - viii -

Fig. Page 23. Lateral view of the thorax of Rhagio scolopaceus 100

24. Lateral internal view of the thorax of R. scolopaceus 101

25. a. Lateral view of the thorax of Hilarimorpha sidora 102 b. Lateral view of the thorax of Vermileo sp.

26. Probasisternal variation in Rhagionidae 103 a. Rhagio scolopaceus b. Atherix ibis c. Chrysopilus cristatus d. Vermileo sp.

27. Prephragmal variation in Rhagionidae 104 a. Rhagio. scolopaceus b._ Atherix ibis c. Chrysopilus cristatus d.. Vermileo sp.

28. a. Posterior internal view of the prephragma of Hilarimorpha sidora 105 b. Ventral view of the probasisternum of H. sidora

29. Lateral view of the thorax of Exhyalanthrax lugens 106

30. Lateral internal view of the thorax of E. lugens 107

31. Thorax of Systropus edwardsi 108 a. Lateral view b. Posterior view of the metathorax

32. Ventral view of the cervix and probasisternum 109 a. Exhyalanthrax lugens b. Bombylius major

33. Ventral view of the cervix and probasisternum a. Enica longirostris b. Callostoma fascipennis - IX -

Fig. Page 34. Probasisternal variation in Bombyliidae 111 a. Heterotropus indicus b. Systropus edwardsi

35. Prephragmal variation in Bombyliidae 112 a. Bombylius major b. Bombylius discoideus c. Callostoma fascipennis d. Usia aenea e. Toxophora maculata f. Phthiria gaedii

36. Prephragmal variation in Bombyliidae 113 a. Exhyalanthrax lugens b. Exoprosopa minos c. _ Villa sexfasciata d. Heteralonia megerlei e. Tomomyza pictipennis f. Anthrax pithecius

37. Pterothoracic furca in Bombyliidae 114 a. Systropus edwardsi b. Exhyalanthrax lugens

38. Metafurcal variation in Bombyliidae 115 a. Bombylius discoideus b. Bombylius major c. Exoprosopa aurulans d. Exoprosopa louisae

39. Metafurcal variation in Bombyliidae 22.6 a. Usia aenea b. Toxophora maculata c. Phthiria gaedii d. Tomomyza pictipennis

40. Lateral view of the thorax of Ogcodes gibbosus

41. Ventral view of the thorax of Qgcodes gibbosus hq - IX -

Fig. Page

42. Probasisternal variation in Acroceridae 119 a. Eulonchus tristis b. Acrocera globulus

43. a,b-prephragmal variation in Acroceridae 120 a. Ogcodes gibbosus b. Acrocera globulus c- Posterior internal view of the metafurca of Ogcodes gibbosus

44. Lateral view of the thorax of Prosoeca accincta 121

45. a. Posterior internal view of the prephragma of Prosoeca accincta 122 b. Ventral view of the probasisternum of Prosoeca accincta

46. a,b- Probasisternal variation in Nemestrinidae 123 a. Fallenia fasciata b. Neorhynchocephalus sulphureus Ch Posterior view of the postphragma of Prosoeca accincta

47. Lateral view of the thorax of Ectyphus pinguis 124

48. Lateral view of the metathorax of Mydas clavatus 125

49. a,b- Prephragmal variation in Mydidae 126 a. Ectyphus pinguis b. Mydas clavatus c- Ventral view of the probasisternum of Ectyphus pinguis

50. Lateral view of the thorax of Scenopinus fenestralis 127 a. External b. Internal

51. a. Posterior internal view of the prephragma of ]_2g Scenopinus fenestralis b. Ventral view of the probasisternum of Scenopinus fenestralis xi

Fig. Page 52. Lateral view of the thorax of Psilocephala sequa 129

53. a,b- Prephragmal variation in Therevidae 130 a. Psilocephala sequa b. Lindneria sp. c- Ventral view of the profurcaternum of Psilocephala sequa

54. Lateral view of the thorax of Apiocera trimaculata 131

55. a. Posterior internal view of the prephragma of A. trimaculata 132 b. Ventral view of the probasisternum of A. trimaculata

56. Posterior internal view of the right ventral metapleural arm in some Brachycera 133 a. Prosoeca accincta b. Ectyphus pinguis c. Psilocephala sequa d. Apiocera trimaculata

57. Lateral view of the thorax of Machimus atricapillus 134 a. External b. Internal

58. Sternum of M. atricapillus 135 a. Ventral view b. Dorsal internal view

59. Thorax of Lgptogaster cylindrica 136 a. Lateral view b. Posterior view of the metathorax

60. Probasisternal variation in Asilidae 137 a. Ommatius parvulus b. Willistonia nigrofemorata c . Efferia albibarbis d. Cophura arizonensis xii -

Fig. Page 61. probasisternal variation in Asilidae 138 a. Zabrops t. tagax b. Atoniomyia duncani c. Triclis sp. d. Laphria columbica e. Leptogaster cylindrica f. Haplopogon erinus

62. prephragmal variation in Asilidae 139 a. Efferia albibarbis b. Qmmatius parvulus c. Laphria columbica d. Ospirocerus abdominalis e. Zabrops j:. tagax f. Willistonia nigrofemorata

63. prephragmal variation in Asilidae 140 a. Machimus atricapillus b. Hodophylax tolandi c. Haplopogon erinus d. Atomosiella antennata e. Blepharepium vorax f. Leptogaster cylindrica

64. a. lateral internal view of the pterothoracic furcae of M. atricapillus 141

b. posterior internal view of the metathorax of M. atricapillus

65 lateral view of the thorax of Empis Livida 142 a. external b. internal

66. dorsal internal view of the thorax of E. livida 143

67. lateral view of the thorax in some Empididae 144 xiii

Page a. Chelifera praecatoria b. Drapetis laevis

68. probasisternal variation in Empididae 145 a. Clinocera stagnalis b. Phyllodromia melanocephala c. Empis livida d. Trichopeza longicornis

69. a,b prephragmal variation in Empididae 146 a. Empis livida b. Clinocera stagnalis

c.d,e,f metafurcal variation in Empididae c. Empis livida d. Clinocera stagnalis e. Platypalpus pallidiventris f. Ocydromyia glabricula

70. lateral view of the thorax of Poecilobothrus nobilitatus 147

71. lateral internal view of the thorax of P. nobilitatus 148

72. sternum of P. nobilitatus 149 a. ventral view b. dorsal internal view

73. probasisternal variation in Dolichopodidae 150 a. Australiola zonatus b. Argyra diaphana c. Machaerium maritimae d. Campsicnemis curvipes e. Liancalus virens f. Medetera truncorum - xiv -

Page 74. prephragmal variation in Dolichopodidae 151 a, Peocilobothrus nobilitatus b. Liancalus virens c. Argyra diaphana d. Australiola zonatus e. Aphrosylus celtiber f. Medetera truncorum

75. a,b lateral internal view of the pterothoracic furcae in Dolichopodidae 152 a. Poecilobothrus nobilitatus b. Argyra diaphana

c.d lateral internal view of the metapleuron in Dolichopodidae c. Poecilobothrus nobilitatus d. Liancalus virens

76. metafurcal variation in Dolichopodidae 153 a. Aphrosylus celtiber b. Liancalus virens. c. Australiola zonatus d. Medetera truncorum

LIST OF TABLES

Table 1 Terminology of the insect sternum 47

Table 2 Character Summary 73

Table 3 Subfamilies of Bombyliidae 159 - XV -

ABBREVIATIONS abc = abdominal cavity cx = coxa abs = abdominal sternite cxb = coxal base absp = abdominal spiracle daes = dorsal anepisternum abt = abdominal tergite dc = dorsocervicale ac = anterocervicale dlr = dorsolateral scutal ridge aem = anepimeron dls = dorsolateral scutal aemr = anepimeral ridge suture aems = anepimeral suture dpla = dorsal pleural arm aes = anepisternum em = empimeron aesp = anepisternal pad emtb = epimeral tubercle aesr = anepisternal ridge es = episternum aess = anepisternal suture fa = furcal arm afc = anterior furcal cup fp = furcal spur afl = anterior furcal limb fpt = furcal pit an^ = antepronotum fs = furcasternum an^ = metascutum hi = haltere anwp = anterior notal wing process isr = intersegmental ridge aph = prephragma iss = intersegmental suture aphth = prephragmal thread kern = katepimeron apsca = anterior prescuto- Ic = laterocervicale scutal arm lmr = longitudinal median atr = anterior trans-scutal ridge ridge lms = longitudinal median ats = anterior trans-scutal suture suture lscr = lateral scutal ridge ax(4th) = fourth axillary lscs = lateral scutal suture sclerite It = laterotergite axe = axillary cord ltr = laterotergal ridge ba = basalare m = meron baa = basalar apodeme mf = cervical membranous flap bac = basalar cleft mnwp = medial notal wing bs = basisternum process bsca = basisternal carina mt = mediotergite bss = basisternal suture npla = notopleural arm; cc = cervical cavity prealar arm cc = cornicula nplc = notopleural cleft cs = costosternal suture pc = postcervicale xvi

pea = postcervical apodeme sb = subalare pes = preepisternum sc = scutum pfc = posterior furcal cup scl = scutellum pfl = ! posterior furcal limb selp = scutellar spine pla = ! pleural apophysis? se = sella pleural arm or apodeme sp = spiracle : ; plr pleural ridge splr = sternopleural ridge : : pis pleural suture spls = sternopleural suture plwp = pleural wing process sscl = subscutellum : pnx = postpronotum sur = suralare n : : postmetanotum P 3 tga = tergal apodeme pna^ = metanotal arm or apodeme tgf = tergal fissure tgfl = tergal fulcrum pnr = postpronotal ridge tgpt = tergal pit pns = postpronotal suture 1 tgtb = tergal tubercle pnwp = posterior notal wing process tr = transnotal ridge pph = postphragma ts = transnotal suture pphr = postphramal ridge tsclr = trans-scutellar ridge ppsca = posterior prescutoscutal arm tscls = trans-scutellar suture psc = prescutum vc = ventral cervicale pscr = prescutoscutal ridge vis = ventral intersegmental pscs = prescutoscutal suture suture ptr = posterior trans-scutal vp = ventral process; ridge coxal condyle pts = posterior trans-scutal vpla = ventral pleural arm suture or apodeme vtr = ventral transverse ridge vts = ventral transverse suture 1

CONTENTS Page

ABSTRACT iii ACKNOWLEDGEMENT S i v LIST OF FIGURES vi

LIST OF TABLES xiv

ABBREVIATIONS xv I INTRODUCTION 1 II MATERIAL AND METHODS 3 III TERMINOLOGY 10 IV MORPHOLOGY OF THE THORAX 4-8 1. Atvlotus agr.es_tis 4-9 2. Pelecorhynchus fusconiger 52 3* Pantophthalmus tabaninus 53 4- •' Chorisops tibialis 59 5» Xylomya tenthredinoides 55 6. Xylophagus fulgidus 56 7* Coenomyia ferruginea 57 8. Rhagio scolopaceus 58 9. Hilarimorpha sidora 59 10 * Exhyalanthrax lugens 60 11 * Systropus edwardsi 62 12. Ogcodes gibbosus 62 13. Prosoeca accincta 63 14-. Ectyphus pinguis 64- 15. Scenopinus fenestralis 65 16. Psilocephala sequa 66 17• Apiocera trimaculata 67 18. Machimus atricapillus 68 19. Empis livida 70 20. Poecilobothrus nobilitalus 71 Figures 78 V SYSTEMATIC SURVEY 154-

TABANIDAE 155 Page

STRATIOMYIDAE 156 RHAGIONIDAE 158 BOMBYLIIDAE ACROCERIDAE 166 NEMESTRINIDAE 167 MYDIDAE 168 ASILIDAE 170 EMPIDIDAE 172 DOLICHOPODIDAE 17^- VI DISCUSSION 178 VII BUMMARY 192 VIII .REFERENCES 195 I INTRODUCTION

"In general, the families of Brachycera are the most disctinctive of Diptera and can be recognised at sight" (Oldroyd, 1969). Despite the authenticity of this statement, both the systematics and the phylogenetic relationships of these families are still problematic (McAlpine, 1979); families are continually split and regrouped and views regarding routes of their evolution are a matter of contention.

The characters most frequently used in the classification of the Brachycera are those of the head, terminalia and wing venatation as well as the chaetotaxy of the legs and thorax. Hardy (1948) has suggested a classification of the Asilidae based on the prothoracic basisternum but the reliability of this criterion was disputed by Clements (1951) and Hull (1962). Se'guy (1926-1928) and Nagatomi (1977) have used some thoracic landmarks, e.g. the trans-scutellar suture, length to width ratio of the scutellum and shape of the mesanepisternum, for generic differentiation. The importance of the cervical and prothoracic sclerites in Diptera has been stressed by Crampton (1926b), and the detailed work of Speight (1969) on the probasisternum of Acalypterate Diptera demonstrates the potential value of this character both in systematics and phylogeny.

Young (1921) has examined representatives of the major families of Brachycera but he only considered the mesothorax and metathorax. His discussion was, however, rather general and his figures were too small to be examined easily. Ulrich's (1971) study on the thoraces of Dolichopodidae and Empididae represents the best account available on these Diptera* Marina & Negrobov (1977, 1980) have studied in great detail many thoracic structures of the Dolichopodidae. Detailed studies of the thoracic skeleton of individual species of Brachycera include those on Tabanus (Bromley, 1926; Bonhag, 1949) and Asilus (Sara & Smerdel, 1953), but - 2 -

a comparative study of the thoracic morphology of the Brachycera as a group is lacking.

The objectives of this research are: 1. To present a detailed account of thoracic skeletons of representatives of the major families of Brachycera. 2. To assess the potential use of thoracic structures in solving problems of Brachycera classifications. 3. To determine the homologies of sclerites and provide a system of nomenclature based on current morphological theory.

The species selected for detailed study were chosen solely because of their availability and not because they are typical of their respective families; selecting a species typical of a highly diverse family is almost impossible and it is meaningless to speak of a typical species when treating a homogeneous family.

In naming sclerites, an effort has been made to adopt a nomenclature that would conform with views of morphologists and care has been taken to ensure that individual sclerites have been given the same names in all species described here. - 3 -

II MATERIAL AND METHODS

Below is a list of species examined during the present investigation, with the genera arranged alphabetically:

1. Ablautus mimus Osten-Sacken, 1877 Asilidae) 2. Acrocera globulus (Panzer, 1803) Acroceridae) 3. Adersia oestroides (Karsch, 1888) Tabanidae) 4. Amictus validus Loew, 1869 Bombyliidae) 5. Ancala africana (Gray, 1832) Tabanidae) 6. A. fasciata nilotica (Austen, 1907) ) 7. Anthrax pithecius (Fabricius, 1805) Bombyliidae) 8. Antonia suavissima (Loew, 1856) ) 9. Aphrosylus celtiber Haliday, 1855 Dolichopodidae) 10. Apiocera aldrichi Painter, 1938 Apioceridae) 11. A. haruspex Osten-Sacken, 1877 12. A. painteri (Cazier, 1941) 13. A. trimaculata Painter, 1938 14. Argyra argentina (Meigen, 1824) Dolichopodidae) 15. A. argyria (Meigen, 1824) ) 16. A. diaphana (Fabricius, 1795) 17. A. leucocephala (Meigen, 1824) 18. A. vestita (Wiedemann, 1817) 19. Asilus vescus (Hine, 1918) Asilidae) 20. Atherix ibis (Fabricius, 1798) Rhagionidae) 21. Atomosia melanopogon (Hermann, 1912) Asilidae) 22. Atomosiella antennata (Banks, 1920) ) 23. Atoniomyia duncani (Wilcox, 1937) ) 24. Atylotus agrestis (Wiedemann, 1828) Tabanidae) 25. Australiola zonatus (Parent, 1932) Dolichopodidae) 26. Backomyia hanni (Wilcox & Martin, 1937) Asilidae) 27. Beameromyia lacinia Martin, 1937 ) 28. Beris chalybeata (Forster, 1771) Stratiomyidae) 29. Bicellaria sulcata (Zetterstedt, 1892) Empididae) 30. Blepharepium cajennensis (Fabricius, 1787) (Asilidae) 31. B. vorax Curran, 1942 ) 32. Bombylius discoideus Fabricius, 1794 Bombyliidae) 33. B. major Linne, 1758 ) 34. B. ornatus Wiedemann, 1828 - 4 -

35. Callostoma fascipennis Macquart, 1840 (Bombyliidae) 36. Campsicnemis curvipes (Fallen, 1823) (Dolichopodidae) 37. Cephalocera longirostris (Wiedemann, 1830) (Mydidae) 38. Cephalodromia fusca (Seguy, 1938) (Bombyliidae) 39. Cerotainiops abdominalis (Brown, 1897) (Asilidae) 40. Chelifera praecatoria (Fallen, 1815) (Empididae) 41. Chloromyia formosa (Scopoli, 1763) (Stratiomyidae) 42. Chorisops tibialis (Meigen, 1822) ( » ) 43. Chrysopilus cristatus (Fabricius, 1787) (Rhagionidae) 44. Chrysops brucei Austen, 1907 (Tabanidae) 45. Chrysotus neglectus (Wiedemann, 1817) (Dolichopodidae) 46. Clinocera stagnalis (Haliday, 1833) (Empididae) 47. Coenomyia ferruginea (Scopoli, 1763) (Coenomyiidae) 48. Coleomyia setigera (Cole, 1919) (Asilidae) 49. Conophorus fuliginosus (Wiedemann, 1820) (Bombyliidae) 50. Cophura arizonensis (Schaeffer, 1916) (Asilidae) 51. Cytherea obscura Fabricius, 1794 (Bombyliidae) 52. Dasyrhamphis ater (Rossi, 1790) (Tabanidae) 53. Dicropaltum mesae (Tucker, 1907) (Asilidae) 54. Dolichocephala irrorata (Fallen, 1815) (Empididae) 55. Dolichopus atripes Meigen, 1824 (Dolichopodidae) 56. D. ungulatus (Linne, 1758) ( " ) 57. D. wahlbergi Zetterstedt, 1848 ( » ) 58. Drapetis laevis Becker, 1913 (Empididae) 59. Ectimus gracilis Loew, 1844 (Bombyliidae) 60. Ectyphus pinguis Gerstaecker, 1868 (Mydidae) 61. Efferia aestuans (Linne, 1767) (Asilidae) 62. E. albibarbis (Macquart, 1849) ( " ) 63. E. tricella (Bromley, 1951) ( " ) Empis' livida Linne, 1758 (Empididae) 65. Empidideicus turneri Hesse, 1938 (Bombyliidae) 66. Enica longirostris (Wiedemann, 1819) ( " ) 67. Eucyrtopogon nebulo (Osten-Sacken, 1877) (Asilidae) 68. Eulonchus tristis Loew, 1872 (Acroceridae) 69. Exhyalanthrax lugens (Loew, 1860) (Bombyliidae) 70. Exoprosopa argentifrons Macquart, 1855 ( " ) 71. E. aurulans Bezzi, 1924 ( " ) 72. E. louisae Francois 1962 ( " ) 73. E. minos (Meigen, 1804) ( " ) - 5 -

74-. Fallenia fasciata (Fabricius, 1805) Nemestrinidae) 75. Geron longirostris Efflatoun, 194-5 Bombyliidae) 76. G. nasutus Bezzi, 1924- ) 77. Gonarthrus cylindricus (Bezzi, 1926) ) 78. G. leucomelas Bowden, 1975 ) 79. Haematopota patellicornis (Enderlein, 1925) Tabaniclae) 80. Haplopogon erinus Pritchard, 194-1 Asilidae) 81. Hercostomus brevicornis (Staeger, 184-2) Dolichopodi&ae) 82. Hermetia illucens (Linne, 1758) Stratiomyidae) 83. Heteralonia megerlei (Meigen, 1820) Bombyliidae) 84-. H_. oculata (Macquart, 184-0) ) 85. Heterotropus indicus Nurse, 1920 ) 86. Hilara pilosa Zetterstedt, 184-2 Empididae) 87. Hilarimorpha sidora Webb, 1974- Hilarimorphidae) 88. Hodophylax tolandi Wilcox, 1961 Asilidae) 89. Holcocephala abdominalis" (Say, 1823) " ) 90. Hybos culiciformis (Fabricius, 1775) Empididae) 91. Hydrophorus sp. Dolichipodidae) 92. Itolia maculata Wilcox, 1936 Asilidae) 93. Lampria rubriventris (Macquart, 1834-) ) 94-. Laphria columbica (Walker, 1866) ) 95. Legnotomyia trichorhoea (Loew, 1855) Bombyliidae) 96. Leptogaster cylindrica de Geer, 1776 Asilidae) 97. L. hesperis Martin, 1957 ) 98. Liancalus virens (Scopoli, 1763) Dolichopodidae) 99. Ligyra paris (Bezzi, 1923) Bombyliidae) 100. Lomatia sabaea (Fabricius, 1781) ) 101. Machaerium maritimae Haliday, I832 Dolichopodidae) 102. Machimus adustus Martin, 1975 Asilidae) 103. M. atricapillus (Fallen, 1814-) ) 104-. M. notialis Martin, 1975 ) 105. Mallophora fautricoides Curran, 1930 ) 106. Medetera truncorum Meigen, 1824- Dolichopodidae) 107. Megapalpus capensis (Wiedemann, 1824-) Bombyliidae) 108. Megaphorus pulchrus Pritchard, 1935 Asilidae) 109. Merosargus stamineus Fabricius, 1805 Stratiomyidae) 110. Microchrysa deannulata Lindner, 1935 ) 111. Mydas clavatus (Drury, 1773) Mydidae) 112. M. ventralis abdominalis Gerstaecker, 1868 " ) 113. Mythicomyia pusillima Edwards, 1930 Bombyliidae) - 6 -

114. NannncvrtQDQgon 1estomviformis (Asilidae) Wilcox & Martin, 1936 115 r Negasilus belli Curran, 1934 ( " ) 116. Nemomvdas nantherinus (Gerstaecker, 1868) (Mydidae) (Tabanidae) 117. Nemorius vitripennis (Meigen, 1820) (Nemestrinidae) 118, Neorhynchocephalus sulphureus (Wiedemann, 1830) (Dolichopodidae) 119. Neurigona pallida (Fallen, 1823) 120, Nicocles argentatus (Coquillett, 1893) (Asilidae) 121. Ocydromyia glabricula (Fallen, 1816) (Empididae) 122. Ogcodes gibbosus (Linne, 1961) (Acroceridae) (Asilidae 123. Ommatius macquarti Bezzi, 1908 124. 0. parvulus Schaeffer, I98I 125. 0_. variabilis Engel, 1929 126. Qmniablautus nigronotum (Wilcox, 1935) 127. Ospirocerus abdominalis (Say, 1824) (Stratiomyidae) 128. Oxycera formosa Meigen, 1822 ( - ) 129. 0. pulchella Meigen, 1822 130. 0. terminata Meigen, 1822 ( > ( - ) 131. Pachygaster atra (Panzer, 1803) (Pantophthalmidae) 132. Pantophthalmus tabaninus Thunberg, 1819 (Pelecorhynchidae) 133. Pelecorhynchus fusconiger (Walker, 1848) 134. Petrorossia albula Zaitsev, 1962 (Bombyliidae) 135- Philipomyia aprica (Meigen, 1820) (Tabanidae) 136. Philoliche magrettii (Bezzi, 1901) ( - ) 137. P. rueppellii (Jaennicke, I867) ( - ) 138. Philonicus albiceps (Meigen, 1820) (Asilidae) 139. Phthiria gaedii Wiedemann, 1820 (Bombyliidae) 140. Phyllodromia melanocephala (Fabricius, 1794)(Empididae) 141. Platypalpus pallidiventris (Meigen, 1822) ( " ) 142. Poecilobothrus nobilitatus (Linne, 1767) (Dolichopodidae) 143. Polacantha compositus (Hine, 1918) (Asilidae) 144. Proctacanthella latruncula (Williston,1885)( " ) 145. Proctacanthus occidentalis Hine, 1911 (Asilidae) 146. Prolatiforceps fulviventris (Shaeffer,1916)( " ) 147. Prosoeca accincta (Wiedemann, I830) (Nemestrinidae) 148. Pseudatrichia punctulata Hardy, 1944 (Scenopinidae) 149. Pseudonomoneura hirta (Coquillett, 1904) (Mydidae) 150. Psilocephala sequa Walker, 1852 (Therevidae) 151. Psilodera confusa Schlinger, 1961 (Acroceridae) t - 7 -

152. Ptecticus testaceus (Fabricius, 1805) Stratiomyidae) 153. Rhagio scolopaceus (Linne, 1758) Rhagionidae) 154.. R. tringarius (Linne, 1758) ) 155. Rhamphomyia variabilis (Fallen, 1815) Empididae) 156. Scenopinus fenestralis (Linne, 1758) Scenopinidae) 157- Sciapus platypterus (Fabricius, 1805) Dolichopodidae) 158. Scleropogon picticornis Loew, 1866 Asilidae) 159. Silvius alpinus (Scopoli, 1763) Tabanidae) 160. Spogostylum ocyale (Wiedemann, 1828) Bombyliidae) 161 • Stratiomys chamaeleon (Linne, 1758) Stratiomyidae) 162. Symphoromyia crassicornis (Panzer, 1807) Rhagionidae) 163. Sympycnus desoutteri Parent, 1925 Dolichopodidae) 164-. Synechus pyramidatus Bezzi, 1905 ) 165. Syntormon pallipes (Fabricius, 1794-) ) 16'6. Systenus adpropinquans (Loew, 1857) ) 167. S.ystropus edwardsi Brunetti, 1920 Bombyliidae) 168. Tabanus biguttatus Wiedemann, 1830 Tabanidae 169. T. gratus Loew, 1860 170. T. guineensis Wiedemann, I83O 171. T. par Walker, 1854- 172. T. sufis Jaennecke, I867 173. T, taeniola Polisot de Beauviour, 1787 174-. Tachytrechus tesselatus (Macquart, 184-2) Dolichopodidae) 175. Teuchophorus spinigerellus (Zetterstedt, ) 176. Thereva annulata (Fabricius, 1805) Thereyidae) 177. Thyridanthrax fenestratus (Fallen, 1814-) Bombyliidae) 178. Tomomyza pictipennis Bezzi, 1921 ) 179.. Toxophora albivittatus Bowden, 1964- ) 180. T. maculata (Rossi, 1790) ) 181. Trichopeza longicornis (Meigen, 1822 ) Empididae) 182. Triclis sp. Asilidae) 183. Usia aenea (Rossi, 1790) ) 184-. Vanoyia tenuicornis (Macquart, 1834-) Stratiomyidae) 185* Vermileo sp. Rhagionidae) 186. Villa sexfasciata (Wiedemann, 1821) Bombyliidae) 187. Wilcoxia martinorum Wilcox, 1972 Asilidae) 188. Willistonia nigrofemorata Wilcox, 1935 ) 189. Xanthochlorus tenellus (Wiedemann, 1917) Dolichopodidae) 190. Xylomya tenthredinoids (Wulp, I867) Xylomyidae) - 8 - i

191. Xylophagus fulgidus Webb, 1979 (Xylophagidae) 192. Zabrops t. tagax (Willis-ton, 188*0 (Asilidae)

Adults of Chorisops tibialis, Rhagio scolopaceus, Leptogaster cylindrica, Machimus atricapillus, Empis livida, Dolichopus Wahlbergi, Hercostomus brevicornis and Peociloboth- rus nobilitatus were collected by me at Wimbledon Common and Silwood Park during July and August both in 1979 and 1980. These were killed in ethyl acetate vapour and stored in 70$ alcohol. The remainder of the material was obtained from various sources (briefly acknowledged elsewhere). These con- sisted of identified pinned specimens.

In order to prepare the insects for study, both the dried and alcohol-preserved specimens were cleared by soaking in a 10% solution of potassium hydroxide for a period of a few hours to several days. It was found that boiling resulted in an unevenly macerated and pitted cuticle. To prevent the continuous corrosive action of the potassium hydroxide, the cleared material was repeatedly washed in water.

The examination of transparent structures was facilitated by staining these in a 0.5%> aqueous solution of mercurochrome for about 12 hours.

The prepared specimens were transferred to alcohol, either: a. 70%> alcohol or b. absolute alcohol from which they were subsequently transferred to terpineol.

Either medium could be used both for examination and storage. Terpineol was found to be superior to 70$ alcohol because the specimens remained clear and the medium did not evaporate. However, specimens stored in it for long periods soon became brittle and could not be further dissected.

The insects were examined under a M5 Wild binocular - 9 - i microscope in a solid watchglass. They were enmeshed in cottonwool to prevent drifing. For the study of internal structures, either a longitudinal or transverse section was made or alternatively the dorsal disc was removed. Drawings were made with the aid of camera lucida. - 10 - i

III TERMINOLOGY: ORIGIN AND DEFINITION OF TERMS USED IN DESCRIBING THORACIC STRUCTURES OF DIPTERA

1. The Cervix

CERVIX: Loew (1862) used the designation "cervix" for the constricted occipital region of the head, while he referred to the neck region as the "collum", a term first introduced by Knoch in 1801 for the prothorax. MacGillivary (1923) and Snodgrass (1835)» among other authors, named the neck region the cervix. Crampton (1909) proposed the term "cervicum" for the neck and was followed by Imms (1925) • Later, Crampton (1942) admitted that the designation cervix would gain general acceptance and should be restricted to the neck region, as is now the case.

CERVICALIA: Embedded in the flexible membranous walls of the cervix are a variable number of sclerites that support the head and provide points of attachment for muscles, while the flexible part permits freedom of motion of the head. Of these sclerites, there may be two dorsal and three on each side. Ventral plates are not common in the Diptera.

Newport (1839) proposed that the neck plates are detached portions of the prothorax and called them the "para- ptera", His views were later adopted by Lowne (1890), who referred to the lateral sclerites as the "condyles". Huxley (1877) regarded the neck as labial in origin and designated its plates by the term "cervical sclerites". His views - 11 - i regarding "the origin of the neck were elaborated by Comstock & Kochi (1902), who argued that the labial appendages have migrated forwards to contribute to the formation of the mouth parts, while the body of the labial segment forms the neck and its sclerites. Crampton (1909) put forth the view that the cervical sclerites are intersegmental in nature, though he admitted that portions of the labial segment may be incorporated in these sclerites. The involvement of both the labium and the prothorax in the formation of the cervical region is generally accepted (Martin, 1916 ; Smreczinski, 1932; Snodgrass, 1935; Henry, 1958; Schmitt, 1959; Matsuda, 1970).

When present, the dorsal cervical sclerites, or "dorsocervicalia" of the Diptera are two in number. They may be strap-like and elongate or may be broad and short, and are situated dorsolaterally. According to Ulrich (1971) each dorsocervicale is provided with a tiny muscle originating on the prephragma, and when the sclerites are absent, the muscles are attached to the dorsal cervical membrane or to the back of the head. Crampton (1926b) found that the dorsocervicalia of Periplaneta act as points of insertion of some muscles. Owen (1977) found that in the mosquito Culiseta a pair of muscles originating on the prephragma is inserted on the dorsolateral surface of the cervical membrane.

On each side of the cervix, there are always three lateral cervical sclerites in the Diptera. From the front backwards, these are the anterior, lateral and posterior cervicale or the antero-, latero- and postcervicale, I -Ir-

respectively . The "ariterocervicale" is generally a small, apodeme-like plate lying alongside the upper margin of the laterocervicale. Anteriorly, it is articulated with the postoccipital condyle of the head. The "laterocervicalia" which are the principal cervical plates extend ventrolat- eral^. Each consists of a broad base and an anterior process. The base may be subconical or it may be subquadrate. In some groups, it is weakly convex or almost flat, while in others it is strongly convex. The anterior process is either elongate and narrow or short and broad. The posterodorsal angle of the laterocervicale is always inflected, thus forming an internal apodeme. In the majority of Brachycera, the postcervicale extends transversely behind the laterocervicale but in the Bombyliid Anthracinae sensu lata, it extends longitudinally. This sclerite is always articulated at its outer edge with the proepisternum. In surface view, it appears edge on, since it lies along the wall of a transverse depression extending behind the posterior margin of the laterocervicale. Internally, the postcervicale is provided with a transverse ridge but in Dolichopodidae there is a long apodeme instead.

Both the anterior and posterior, cervicale are believed to be detached from the large lateral cervicale (Crampton, 1925, 1942). Matsuda (1970) treated the three sclerites as a single structure and referred to them collect- ively as the lateral cervical sclerite.

In Poecilobothrus, there is a crescentic ventral cervical sclerite extending transversely between the anterior - 13 - i

processes of the laterocervicalia. In many of the lower orders of Insecta, one or more transverse sclerites are present in the ventral area of the cervical region, but among the Brachycera, these are unique to the Dolichopodidae (Ulrich, 1971).

SELLA: Immediately anterior to the probasisternum, there is a raised area carrying a plate whose shape and degree of sclerotisation vary considerably in different Brachycera. Comstock & Kochi (1902) revived MacLeay's (I830) term "presternum" for this plate, which they took as a detached portion of the probasisternum. Martin (1916) accepted Comstock's concept regarding the derivation and nomenclature of this organ and suggested that it is absent in most insects. Crampton (l9*+2) made the same error when he stated "The presternum forms a ventral cervical sclerite in certain Cyclo- rrhapha, but is usually absent in lower Dlptera". Crampton's (1926b) classical work on the cervical and prothoracic sclerites of insects treated this organ very superficially; he indicated the presence of the presternum in only 27 of his 120 figures and failed to notice its presence in Mydas, a genus in which this plate is very prominent and strongly sclerotised. Matsuda's (1970) views with regard to the presternum are rather.-.contradictory ; on p. 19 he accepts the presence of a presternum in Calliphora but on p.307 he denies its presence in Musea and contends that the so-called presternum in this and other Dipteran genera is merely a secondary ventral cervical sclerite. He further claims that the presternum in higher Diptera cannot be homologised with - 14 - i the presternum in the lower orders of Insecta, since this structure, according to his views, is absent in the Nemato- cera and Mecoptera.

In all the Brachycera examined in this study, a more or less differentiated pair of hair bundles is invariably present. Speight (1969), who postulated the possibility of the independent development of the cervical organ (=Sella) and the presternum, has asserted that in Acalypterae these two organs are intimately associated with each other and sometimes even indistinguishably fused together. In Machimus, the two hair bundles are separated from each other by membrane and the area between them and the basisternum is totally membranous, but is slightly raised from the rest of the surrounding membrane and is shiny. In Poecilobothrus, a constriction almost separates the area into an anterior portion carrying the two hair bundles and a posterior part. In all the other Brachyceran species studied, the two components are indistinguishably fused together.

Peters (1962), Speight (1969) and Ulrich (1971) have identified two components in the presternum of older writers. The posterior part is Peters' "presternum". Speight's "presternum" and Ulrich's "praesternum". Peters called the anterior part the "prosternal organ", Ulrich referred to it as the third "ventral cervicale" while Speight introduced for this same part the term "cervical organ". Lowne (1890), in his study of Calliphora, was the first author to describe the morphology and histology of the presternum complex. This structure is saddle-shaped in Calliphora and for this reason - 15 - i

Lowne named it the "sella". Anteriorly, the sella "bears two compact bundles of sensory hairs. The anterior portion of this organ is deflected inwards at a slight angle to the remainder of the plate, so that the hair bundles occur in a depression whose anterolateral walls are formed by two curved lobes that Lowne (op.cit.) called the "corniculae".

Comstock & Kochi (1902) have revived MacLeayfs (1830) term "praesternum" to apply it to a sclerite lying anterior to what they called the sternum (=basisternum) in Pteronarc.ys (Plecoptera) and Gryllus (Orthoptera). Subsequent writers have extended this usage to other orders including the Diptera (Martin, 1916; Crampton, 1926b; Snodgrass, 1935; Bonhag, 1949). The presence of the sensilla has been overlooked and Lowne's description of the sella was apparently neglected. Bonhag (1949) noticed that the presternum of Tabanus received two nerves from the prothoracic ganglion. Thus he was able to attribute a sensory function to that organ but he, presumably, was unable to detect the presence of hairs on its anterior part. Speight (1969) did not give reasons for abandoning Lowne's term "sella" and introducing his own term "cervical organ". In the present work, the whole sclerite that bears the sensilla is designated the sella. The long- used term "presternum" is considered to be a synonym of the sella. - 16 - i

2. The Thorax

The modern terminology for the thoracic sclerites is based upon the work of Audouin (1824) , who laid the foundations of all subsequent work on the thoracic morphology of insects. This author believed that the insect thorax is composed of three simple segments which he designated the pro-, meso- and metathorax, terms first proposed "in 1818 by Nitzsch, who used the term "protothorax" instead of "prothorax". Accord- ing to Audouin (1824-), each thoracic segment consists of a dorsal "tergum", two lateral "plurae" and a ventral "sternum". He regarded the tergum of a wing-bearing segment as formed, from the front backwards, of the "praescutum", "scutum", "scutellum" and "postscutellum". In the pleuron, he recognised two major plates, an anterior "episternum" and a posterior "epimeron". He thought the sternum comprises a single plate. MacLeay (1830), basing his argument on the condition found in the tergum, assumed that the sternum consists of the "praesternum", "sternum", "sternellum" and "poststernellum". His views were unfavourably criticised by Crampton (1909) as discussed laterCp*3S)-

TERGUM: The term "dorsum" is applied to the whole dorsal surface of an insect's body. The entire dorsal region of a segment is the "tergum" or "notum". A subdivision of the tergum is a "tergite"

In Diptera, Mecoptera and certain Hymenoptera, the prothoracic tergum or "pronotum" is divided by a transverse suture into an anterior and posterior part. In all other - 17 - i orders of Insecta, the pronotum is a single plate (Crampton, 1926b; Matsuda, 1970). The bipartite nature of the Dipteran pronotum was recognised by Lowne (I890) who, in his work on Calliphora, designated the anterior part as the "prodorsal arch" or "prodorsum" and the posterior one as the "paratreme". He homologised the paratreme with the humerus of other writers. This author, and before him Hammond (1881), considered the muscles of the fore coxa to be inserted on the humeral callus, which he took as proof of the prothoracic nature of this sclerite. The findings of £alokar (1947), Miller (1950) and Speight (1969) support Lowne's claim. The humeral callus is also taken to be prothoracic by Crampton (1925, 1942), Bromley (1926), Snodgrass (1935). Bonhag (1949), Sara & Smerdel (1953). Matsuda (1970), Ulrich (1971) and Imms (1977). Ferris (1950) considered the humeral callus as part of the mesothoracic prescutum.

Lowne (I890) contended that the pronotal sclerites could not be homologised with the highly modified sclerites of the mesonotum. Snodgrass (1927) expressed similar views when he stated that none of the prothoracic characters are homologous with the pterothoracic structures. This author believed that the prothoracic tergum always lacks a true antecosta and precosta, which parts he thought have been lost in the neck. Crampton (1909) claimed that the structure of the pronotum conforms with the same basic plan as that of the pterothoracic terga. However, he admitted the fact that neither a prescutum nor a postscutellum has ever been identified in the prothorax, suggesting that these sclerites were either lost through reduction or fusion with the scutum and - 18 - i scutellum, or never existed in the prothorax. Later, Crampton (1925) designated the two pronotal plates of the Diptera as the anterior and posterior pronotum or "antepronotum" and "postpronotum" , respectively. This terminology has gained wide acceptance among students of the Diptera, but some systematists still adhere to the familiar term "humeral callus", which is part of Crampton's postpronotum. Zalokar (194-7) used the terms prescutum and scutum for the two pronotal sclerites. Imms (1977) called these plates the scutum and scutellum in Tipulidae. In the present account, Crampton's terminology of antepronotum and postpronotum is adopted.

The antepronotum and postpronotum are separated by a transnotal suture that continues downwards into the propleural suture. The antepronotum forms a dorsal collar and extends laterally, on each side, to meet the proepisternum at the point where the apex of the laterocervicale arti- culates with the prothorax. This is the delimitation of the antepronotum as defined by Crampton (1925, 194-2) and Bromley (1926). Bonhag (194-9), Sara & Smerdel (1953), Speight (1969) and Ulrich (1971) restricted the antepronotum to the transverse sclerite occupying the dorsal anterior margin of the thorax and considered the sclerites extending lateral to it as parts of the proepisternum. Matsuda (1970) claimed that the transverse sclerite in the mid-dorsal area is the mesothoracic acrotergite. According to his views, the'antepronotum consists of the lateral plate extending between the acrotergite and the proepisternum, on each side. Owen (1977) accepted Matsuda's interpretation of the acrotergite and the - 19 - i antepronotum.

In certain Tipulidae, as in Limnophila, the two pronotal sclerites lie clearly anterior to the mesonotum; in many other Nematocera the pronotum is pressed downwards by the greatly enlarged anterior part of the mesonotum, but the dorsal part of the postpronotum is still present as a very narrow band of integument. In the Brachycera as well as in the Cyclorrhapha, the intrusion forwards of the mesonotum is more advanced. As a result of this, the postpronotum becomes divided into two isolated lobes occupying the anterolateral angles of the greatly developed mesonotum. Matsuda has gone too .far to claim that the enlarged mesonotum has completely excluded the pronotal elements from the dorsal part of the thorax. I believe that the anterior margin of the thorax is formed by the antepronotum and not by the acrotergite.

The postpronotal lobes may be conspicuously swollen and in some groups their posterior margins are more or less truncate. In other groups, they are almost flat, but the sutures delimiting them from the mesonotum are almost always retained, Ventrally, they are often united with the proepimeral sclerites. A vertical suture may extend downwards from the posterior margin of the postpronotum to separate this plate from the spiracular sclerite. When such a suture exists, it is taken as the anterior intersegmental suture that separates the prothorax from the mesothorax.

According to Audouin (1824), the tergum of a wing- bearing segment consists of a "prescutum", "scutum", \ - 20 - i

"scutellum" and "postscutellum". Audouin's concept of the division of the wing-bearing segment is obsolete but his terminology for the subdivisions of these regions is still accepted by the majority of entomologists. In his discussion of the thoracic sclerites of insects, Crampton (1909) considered the scutum and scutellum as the major components of the tergum of a wing-bearing segment. He proposed that the prescutum and postscutellum usually occur as phragmata, except in the Diptera, where the mesothoracic postscutellum may be largely external. Later, Crampton (1914a) divided the tergum into a wing-bearing "scutoscutellum" and a phragma- bearing "postscutellum". Martin (1916) suggested that the tergum consists of a single undivided plate, the scutoscutellum. He postulated that the postscutellum is a secondary development accompanying the development of the wings, thus accepting Snodgrass' (1909) view of the secondary nature of this plate. However, he strongly criticised the introduction by Snodgrass of the term "postnotum" as substitute for Audouin's term "postscutellum". Snodgrass (1935) divided the tergum into a wing-bearing "alinotum" and a phragma- bearing "postnotum". The first of these terms is synonymous with Crampton's scutoscutellum and the second with Audouin's postscutellum. While Audouin assumed that the postscutellum is a segmental sclerite, Snodgrass claimed that the postnotum is a secondary sclerite developed as a result of the expansion forwards of the acrotergite of the following segment. This view is a corollary of Snodgrass' (1927) theory of secondary segmentation of the insect body. The theory is based on the assumption that the modern hard-shelled arthropods - 21 - i have evolved from soft-skinned segmented ancestors in which the principal longitudinal muscles are inserted on intersegmental soft rings. During the hardening of the body walls, the posterior part of each segment remained flexible to act as its movable joint. These areas of flexibility became the functional intersegmental membranes, while the primary intersegmental rings have become hardened and con- verted into internal ridges, or "antecostae", marked externally by corresponding antecostal sutures. From each antecosta is developed an internal plate-like apodeme, or "phragma", that gives attachment to the greatly enlarged longitudinal muscles of the wing-bearing segment. Between each antecostal suture and the secondary intersegmental membrane anterior to it, there is a narrow rim, or "precosta" belonging to the segment preceding. When the intersegmental membrane persists, the precosta forms the "acrotergite" of the segment following and the phragma arising from the antecosta behind it is regarded as a "prephragma". When the precosta expands forwards into the intersegmental membrane, the enlarged plate forms the "postnotum" of the segment preceding and the phragma that continues from its posterior margin is considered a "postphragma".

In his definition of intersegmental sclerites, Snod- grass (1927) states: "The only true "intersegmental" elements, however, are the antecostae or parts derived from them, such as the phragmata of the dorsum ..... Most other so-called "intersegmental" chitinisations belong either to the anterior or the posterior parts of the true segmental areas". This definition seems to preclude the postnotum - 22 - i

from being intersegmental. This author (loc.cit.; p.7), when enumerating the tergal plates, referred to "a narrow anterior marginal lip, or "precosta", belonging to the segment preceding" (the postnotum is the enlarged precosta). Snodgrass (1935) emphasised the segmental nature of the postnotum when he stated on p.l77s "The elimination of the secondary intersegmental membranes by the enlargement of the acrotergites virtually restores the pterothoracic dorsum to a condition of primary segmentation, since the functional segmental limits are now marked by the primarily intersegmental phragmata. The postnotal plates are thus seen to belong morphologically each to the segment of the tergal plate preceding it". Still later, Snodgrass (1952) stated: "The antecostal sulci mark the true intersegmental lines of the thorax, so that the narrow anterior lip of each groove really belongs to the preceding segment, as does also the functional "intersegmental membrane" before it".

Snodgrass' concept of the intersegmental nature of the postnotum is unnecessarily complicated. The modifications undergone by the tergum seem to be merely a redistribution of some of the primitive elements in a way correlated with the efficiency of muscle movements. Even in groups in which the tergum is highly modified, the dorsal longitudinal muscles still retain their attachment on the antecostae and the antecostal sutures form the true intersegmental lines. As early as 1898, Janet made the observation that "the name" intersegmental membrane generally given to such a membrane (=Snodgrass' intersegmental membrane), justified by its - 23 - i physiological function, is however, inexact from a morphological standpoint". In the present work, the postnotum is taken to be a segmental plate belonging to the segment preceding .

In the mesothoracic tergum of the Diptera, we expect to find an acrotergite, which morphologically is part of the pronotum, a prescutum, a scutum, a scutellum and a postnotum or postscutellum. The acrotergite forms a very narrow lip extending anterior to the antecostal suture to connect the antecosta with the pronotum. In Tipula (Snodgrass, 1935; Matsuda, 1970), the acrotergite is present as a narrow marginal band and is separated from the pronotum by a narrow membrane. In the Brachycera, the acrotergite is not per- ceptible. Matsudafs (1970) interpretation of the acrotergite in Tabanus is erroneous as already discussed.

In Tipula (Crampton, 1925; Snodgrass, 1927), the prescutum is represented by a very narrow portion extending transversely in front of the scutum and two lateral portions (one on each side) extending backwards on the sides of the scutum to end near the bases of the wing. Crampton referred to the transverse portion as the "pretergite" and called the lateral portion the "paratergite". Snodgrass (1927) homologised both areas with the prescutum. In the higher Diptera the prescutum is not discernible anteriorly but its rem- nants extend lateral to the scutum, terminating in the prealar arms in front of the wing bases. The prealar arms continue ventrally and come into contact with the dorsal edges of the anterior basalares, thus forming bridges that connect - 24 - i the tergum with the pleuron. Snodgrass' concept of the prescutum, which is adopted in this investigation, has been accepted by Bonhag (194-9), Sara & Smerdel (1953), Matsuda (1970) and Owen (1977).

The higher Diptera represent a high degree of modification which has obscured the relation between different skeletal parts. As already mentioned, both the postpronotum and the mesothoracic prescutum have lost their dorsal continuity and are represented by laterally situated plates and the acrotergite has lost its individuality. In more generalised insects, the three regions may be present as distinct plates, with the postpronotum and the acrotergite extending in front of the antecostal suture and the mesothoracic prescutum behind. If facts are accepted as they are, the higher Diptera seem to present an unusual situation where the antecostal suture extends not between the acrotergite and the prescutum but between the antepronotum and the mesoscutum. The position of the prephragma beneath the antecostal suture is not affected by these modifications. The prephragma which is a plate-like inflection of the antecosta is variable both in shape and size in different groups of the Brachycera. This structure may be greatly enlarged or it may be rudimentary, it may be strongly bilobed or its lateral arms are greatly reduced or even completely lost.

The mesoscutum is the most prominent sclerite of the mesonotum. It may be divided into three longitudinal regions by two dorsolateral longitudinal sutures as in Atylotus and Rhagio. The lateral areas may be divided by - 25 - i two transverse sutures, of which the anterior one arises from the posterior end of the prescutum on each side, while the posterior transverse suture arises from the posterior scutal margin, dorsal to the median notal wing process. The anterior transverse suture is persistent in the majority of Brachycera but it may be greatly reduced or completely lost in a few groups. The lateral scutal margins are highly modified to accommodate the strong flight muscles and support the wings. An oblique suture that appears as a posterior con- tinuation of the prescutoscutal suture sets off a shelf-like marginal sclerite that provides the most anterior articulat- ory point of the wing, the anteriornota'l wing process, Crampton (1914a) called this sclerite the "supra-a]are" but later, Crampton (1914b) referred to it as the "suralare".

The area behind the suralar plate is generally elevated and traversed by a fissure, "tergal fissure" of Matsuda (1970). On the anterodorsal edge of the fissure, there very often occurs an internal apodeme, variously known as the scutal process (Schlein, 1970), scutal apodeme (Ulrich, 1971) and scutellar ridge (Owen, 1977). Bonhag (1949) recognised this apodeme in Tabanus but did not give it a name. In the present account, it is called the "tergal apodeme". Mickoleit (1969) considered this apodeme as a synapomorphic character of the Brachycera but its presence in both Cyclorrhapha and Nematocera is established (Schlein, 1970; Owen, 1977). The depressed area behind the tergal fissure extends laterally to form the median notal wing process.

A V-shaped suture, which has its apex directed forward, - 26 - i

may divide the scutoscutellum or alinotum into the anterior scutum and the posterior scutellum. This suture is generally obliterated or completely lost in most of the Brachycera. A trans-scutellar suture may divide the scutellum into a small anterior part and a large posterior part. The posterior part of the scutellum is differentiated into a median evaginated plate that projects backward above the postnotum. and two lateral depressed areas. The median plate may be greatly prolonged and overgrow the postnotum but there are groups in which it is very short. In some of the Stratiomyidae, the posterior margin of the elevated plate is armed with strongly developed spines. The occurrence of these spines, as well as the width to length ratio of the median plate, is used as q. supplementary character in classifying the Stratiomyidae (Nagatomi, 1977).

On each side of the median scutellar plate, there is an anterior and a posterior ridge. The anterior ridge forms a bridge with the scutum. The posterior ridge forks into an anterior arm that provides the folded posterior notal wing process and a posterior arm that continues into the axillary cord.. Situated between the posterior notal wing process and the axillary cord is a sclerite that appears to be detached from the ventral side of the former. This sclerite is the fourth axillary sclerite of most writers. Matsuda (1970) regarded it as the posterior notal wing process.

The posteriormost region of the mesonotum is the postnotum or postscutellum. According to Snodgrass' theory of secondary segmentation, this plate is the enlarged acrotergite - 27 - i of the metanotum. However, Snodgrass (1935) conceded that the pterothoracic tergum of the Diptera has restored a condition of primary segmentation wherein the antecostal sutures constituted the true intersegmental lines. This author has thus accepted the fact that, at least in the Diptera, the

\ postnotum belongs morphologically to the mesonotum and is not an intersegmental plate. Snodgrass (1927) suggested a code of ethics that demanded of morphologists to retain, when- ever possible, old nomenclature as labels even when the ideas implied in some names are discarded. If this code is strictly observed Audouin's term "postscutellum" should stand regardless of its derivation or the conception it implied. There is, however, a general tendency to abandon Audouin's term in favour of that of Snodgrass (Bonhag, 194-9; Ferris, 1950; Sara & Smerdel, 1953; Matsuda, 1970; Ulrich, 1971 and Imms, 1977). The adoption of Snodgrass' term does not necessarily imply that his theory of the intersegmental origin of the postnotum is accepted; Matsuda has adopted the term postnotum while insisting that it is segmental in nature. On the other hand, Martin (1916) has accepted its intersegmental nature but preferred the appellation postscutellum.

In many Brachycera the postnpfcum is greatly enlarged. It may be divided by a suture on each side into an unpaired median postnotum, the "medio.t'ergite" of Martin (1916) and two lateral postnotal plates, the "laterotergites" of Rees & Ferris (1939). The mediotergite often becomes overgrown by the scutellum but this does not affect the laterotergites, » - 28 -

which may become greatly developed arid conspicuously swollen. In the Stratiomyidae, the anterior part of the mediotergite is differentiated into a strongly convex plate, the "subscutellum" of Crampton (1942). The posterior margin of the mediotergite continues into the postphragma that projects into the body cavity. The laterotergites are separated from the mesepimera by internally ridged sutures and the base of the postphragma turns forwards to unite with the anterolateral edges of these ridges.

The metanotum is greatly reduced and may be concealed by the first abdominal tergite. The rudimentary metanotum consists of the metascutum and the metapostnotum. The metascutum extends as a narrow band between the halteres and bears the notal wing processes. The metapostnotum continues laterally with the metepimera behind the halteres.

PLEURON: The pleuron comprises the sclerites lying between the tergum and the sternum, forming the lateral walls of a thoracic segment. A subdivision of the pleuron is a "pleurite". A pleural suture divides this area into an anterior "episternum" and a posterior "epimeron".

The prothoracic pleural suture, which extends upwards from the coxopleural articulation, divides the propleuron into two simple sclerites, the anterior "proepisternum" and the posterior "proepimeron" . Dorsally, the proepisternum is bordered by the antepronotum, from which it may be delimited by a suture or by an incision or the two sclerites may be fused together. Anteriorly, the proepisternum is always - 29 - i closely associated with the postcervicale. Ventrally, the proepisternum may extend anterior to the coxa to unite with the probasisternum, forming what systematists call a "precoxal bridge". Most families of the Brachycera contain genera in which the proepisternum is connected to the probasisternum by a precoxal bridge. The occurrence of this bridge was used by Malloch (1928) and Hardy (1948) in classifying the Asilidae. Later, it has been shown that the character is quite variable even within subfamilies (Clements, 1951? Hull, 1962).

The term precoxal bridge has been used in various senses and there is no uniformity in applying it. Some authors maintain that it may form a distinct sclerite that persists even when the probasisternum and proepisternum are dissociated (Crampton, 1914a; Martin, 1916; Snodgrass, 1935; Speight, 1969). Sarav & Smerdel (1953) applied the term to the whole anterior area between the proepisternum and the mid-ventral line. Matsuda (1970) claimed that the bridge is formed as a result of the secondary sclerotisation of the episternal membrane. In the present account, the existence of a morphologically distinct precoxale is not accepted. The probasisternum is simply described as either being fused to the proepisternum or separated from it by membrane.

The proepimeron is not always clearly defined, especially posteriorly. In some groups, there is a definite intersegmental suture that extends downwards from the posterior margin of the postpronotum to the posterior margin of the procoxal base, thus marking the boundary between the pro- - 30 - i thorax and the mesothorax. However, this suture is not always present as a distinct line and very often the proepimeron is indistinguishably fused to the mesepisternum.

The proepimeron continues ventrally posterior to the fore coxa to unite with the profureasternum. The two plates may be separated by a sternopleural suture.

In its course from the coxopleural articulation to the wing base, the mesopleural suture takes two angular turns. When the turns are sharp, a horizontal portion of the suture extends between the two angles. This portion may be relatively long or only a short curve. The tortuous mesopleural suture divides the mesopleuron into the anterior "mesepisternum" and the posterior "mesepimeron". When the horizontal portion of the mesopleural suture is long, the lower area of the mesepisternum intrudes into the mesepimeral region. In some groups, this portion is very short and the episternal and epimeral areas extend almost parallel to each other. Systropus presents an extreme of the latter condition, recalling the Nematoceran Diptera.

A subhorizontal suture that appears as a forward con- tinuation of the horizontal portion of the mesopleural suture divides the mesepisternum into an upper plate, the "anepisternum" and a lower plate known variably as the "katepisternum" or "sternopleurite". Ferris (1940a), in his study of P-fcega,r observed an oblique suture arising near the base of the anepisternal suture and extending forwards and downwards to the ventral side of the body, thus dividing the lower mesepisternum into an anterior and a posterior 31 -

plate. Ferris designated this suture the "pleural costa". To the sclerite extending anterior to the suture, he applied the designation "preepisternum" while he termed the plate extending posterior to the suture as the "katepisternum". In his study of Drospphila, Ferris (1950) concluded that the pleural costa has moved posteriorly to correspond with the posterior margin of the episternum, thus leaving the preepisternum anterior to it to comprise the whole ventral episternal area. Hopkins (1909) first introduced the term preepisternum as a substitute for Audouin's (1820) term "hypopteron". Audouin originally proposed the term hypo- teron to designate a narrow sclerite that, in Dytiscus, lies in front of the episternum. Later, Audouin (1824) incorrect- ly included this sclerite together with the tegula under the designation "parapteron" . Subsequent authors have applied the two terms interchangeably and extended their use to other sclerites, as the basalare and the subalare. The need for far more consistent terms was apparent and Hopkins' term preepisternum was immediately accepted by his contemp- oraries. Snodgrass (1909) has correctly applied this term in his figure of Dissosteira but in his other figures he designated different sclerites as the preepisternum. In his study of the thorax of the Hymenoptera, Snodgrass (1910) introduced the term "prepectus" in the belief that, in the Hymenoptera, the sclerite for which he proposed the new name is not homologous with the preepisternum of the more generalised orders of insects. Crampton (1914a) homologised both the preepisternum and the prepectus with Audouin's (1820) hypopteron. Martin (1916) designated as the preepisternum - 32 - i a narrow sclerite set off the anterior margin of the lower metathoracic episternum in Periplaneta. In Tabanus, Snodgrass (1935) divided the lower episternum into a small katepisternum most of which is ventral to the horizontal part of the mesopleural suture, an undefinable mesosternum, and a precoxal bridge connecting the two areas. In groups in which the lower episternum is subdivided by a tranverse suture , Snodgrass (op.cit.). designated the anterior subdivision as the preepisternum, and when this area is united with the sternum, he termed the composite sclerite the prepectus. It is obvious that the term preepisternum has long been used in a similar sense to that in which it has been used by Ferris. The only new introduction by Ferris is the assumption that, in the Diptera, the pleural costa has become confluent with the pleural suture. In all respects the term preepisternum as applied by Ferris is synonymous with the sternopleurite of Osten-Sac'ken (1884) and the katepisternum of other authors, In the present work, Ferris's concept of the preepisternum is adopted.

The anepisternum is separated from the mesoprescutum by a membranous cleft, the "notopleural cleft". This cleft may be continuous with the mesothoracic spiracular membrane or it may be separated from it by a secondary sclerotisation that forms a bridge connecting the anepisternum with the postpronotum. The notopleural cleft is rather broad in Scenopinus; in Chorisops, the cleft is so narrow that it approaches the status of a suture. In some groups, the spiracular membrane is completely sclerotised and the mesothoracic spiracle is borne on the anterodorsal angle of the - 33 - i

composite plate formed by the fusion of the secondarily sclerotised area with the anepisternum. The ventral boundary of the anepisternum is marked by the anepisternal suture of Crampton (1917). Bonhag (194-9) and several other contemporary entomologists have adopted Crampton's terminology for this suture. Matsuda (1970) designated it the "anapleural suture". As the suture dividing the epimeron into the upper anepimeron and the lower katepimeron is also anapleural in nature, it is more convenient to use Crampton's terminology.

When complete, the anepisternal suture extends between the mesopleural suture and the mesothoracic spiracle. This suture may be anteriorly lost or it may be completely absent. In a few groups an oblique suture, which may be a remnant of the intersegmental suture, arises on the anterior part of the anepisternal suture and extends anteroventrally to the posterior margin of the prothoracic coxal base. The edges of the spiracular membrane may approach each other ventrally, thus forming a secondary suture that partly separates the mesepisternum from the proepimeron. In Poecilobothrus, the anepisternum is traversed by an oblique internal ridge that arises near the anterior edge of the anepisternal suture and extends posterodorsally. Ulrich (1971) called this ridge the "anepisternal pad". In Chorisops a similar ridge is present in the anepisternum but it is situated more dorsally. Although this ridge may not be homologous with that in Poecilobothrus, it would be designated as the anepisternal pad. - 34 - i

On the posterodorsal margin of the anepisternum, there are two oval plates which Crampton (1914a) designated as the "basalares". The anterior basalare is delimited from the anepisternum by a suture or a narrow membranous cleft. Apparently, the posterior basalare is separated from the anterior one but an internal apodeme, the "basalar apodeme11 originates from the common wall between the two sclerites.

A transverse membranous cleft, the "basalar cleft" of Matsuda (1970), separates the pleural wing process from the rest of the anepisternal area, to which it belongs. Poster- iorly, the pleural wing process is delimited from the mesepimeron by the mesopleural suture.

Embedded in the soft cuticle between the anepimeron and the posterior part of the wing base is an elongate plate which Crampton (1914a) called the "subalare". This sclerite may be partly fused with the anepimeron or it may be completely detached from it, Crampton (1914a, 1942) and Snod- grass (1927, 1935) considered the subalare as part of the pleuron. Snodgrass (1927) claimed that, in nymphal Orthop- tera, the subalare exists as an undifferentiated part of the pleuron and that, at this stage, the subalar muscle is attached to the upper edge of the pleuron. Maki (1938), who also studied the musculature of several Orthopteran nymphs, presumed that the subalar plate remained as part of the lateral margin of the tergum and that only during the last moulting did the subalare become isolated from the rest of the tergum. Maki's claim is supported by evidence obtained by several authors (Breed, 1903; Khanna, 1963; Chadwick, - 35 - i

1957). Matsuda (1963, 1970) treated the subalare as part of the tergum. Whether the subalare is tergal or pleural in origin is a question yet to be settled but there remains the fact that it is more closely associated with the pleuron than with the tergum.

The "mesepimeron" is the sclerite that extends posterior to the mesopleural suture. An oblique suture that arises near the posterior angle of the mesopleural suture and extends to the base of the laterolergite divides the mesepimeron into a dorsal "anepimeron" and a ventral "katepimeron". The katepimeron is indistinguishably fused with the mesomeron. The dorsal margin of the anepimeron may be interrupted by a vertical fissure. The subalare, when detached from the anepimeron, continues downwards as a narrow arm that fits into this fissure. In Atylotus, the internal ridge arising beneath the fissure continues posteroventrally to almost divide the anepimeron into an anterior and a posterior part. When the subalare is partly fused with the anepimeron, the fissure may be greatly reduced. In Poecilobothrus. the subtriangular laterotergite intrudes anteriorly into the anepimeral area.

As already mentioned, the mesomeron is united with the katepimeron without a suture, thus forming a composite plate that systematists know as the "meropleurite". The composite meral plate may be traversed by a horizontal fissure that partly or completely divides it into an upper and a lower part. This fissure is lacking in a few groups, as in Atylotus and Chorisops. Ventrally, the mesomeron extends - 36 - , to the mid-ventral line to meet its counterpart from the other side of the thorax.

The boundary between the mesomeron and the metepisternum extending posterior to it is marked by the posterior intersegmental suture. This suture may be almost straight or the mesomeron may intrude caudally, thus push- ing the intersegmental suture towards the metapleural suture. The intrusion caudally of the mesomeron reaches its extreme in Poecilobothrus and Empis where the intersegmental suture and the metapleural suture become confluent over a short distance, so dividing the metepisternum into an upper part and a lower part.

The course of the metapleural suture from its pleuro- coxal articulation to the haltere base is nearly vertical "in the majority of the Brachycera. It is not true that, as Young (1921) claimed, either the metepisternum or the metepimeron becomes enlarged at the expense of the other. In both Empis and Poecilobothrus, the metepisternum is reduced as a result of the intrusion caudally of the mesomeron and this seems to apply to other groups in which the metepisternum is reduced. As a result of the shifting forwards of the greatly enlarged metepisternum in S.ystropus, the composite mesomeral sclerite is crowded into a very narrow area above the mesocoxa.

In groups with narrow metepimeral plates, most of the ventral area of the metepimeron remains membranous; the deposition of cuticle in this area results in the enlargement of the metepimeron. Striking examples are those of - 37 - i

Leptogaster and Systropus . In these two genera, the metepimeral sclerites extend ventrally posterior to the hind coxae to meet each other along the mid-ventral line, so forming a complete cone between the metacoxae and the abdomen. Complete sclerotisation of this area occurs in Glossina and Hippobosca (Schlein, 1970).

In Poecilobothrus, the metapleural suture bears two internal apodemal arms. The more ventral one arises at the base of the metapleural ridge and projects into the body cavity as a club-shaped structure. The dorsal arm arises near the dorsal limit of the pleural ridge and projects posteriorly. The occurrence of these arms in Dolichopodidae was established by Ulrich (1971), who considered these structures as apomorphic characters unique to the Dolichopodidae. In Apiocera, the ventral edge of the metapleural ridge is produced into a well developed spatulate arm on which abut the posterior metafurcal limb. In the majority of the Brachycera, a more or less developed flat arm projects internally from the ventral edge of the metapleural ridge. This arm either supports, or gives attachment for muscles originating on the posterior limb of the metafurca. In Empis, a short apodemal arm arises on the dorsal part of the metapleural ridge.

In Mydas, the metepimeron bears an external tubercle. Young (1921) interpreted this structure as arising from the first abdominal tergite. Wilcox & Papavero (1971) accepted this interpretation. However, the metepimeral ridge extends along the anterior margin of the tubercle. As - 38 - i

•the metapleural suture bearing this ridge delimits the metepimeron from the metepisternum anterior to it, there seems little doubt that the tubercle is part of the metapleural area. The fact that the first abdominal spiracle lies posterior to the tubercle gives further support to the view that this structure is metathoracic and not abdominal; according to Young, the first abdominal spiracle is found in the anterior part of the segment or in the membrane between it and the metathorax. The metepimeron extends dorsally behind the haltere to join the metapostnotum.

The basalare and the pleural wing process are closely associated with each other and are embedded in the soft cuticle below the haltere, anterior to the metapleural suture.

The subalare extends along the anterodorsal margin of the metepimeron. In Machimus there is a pit at the base of this sclerite. This pit invaginates to give rise to a short internal apodeme. In Poecilpbothrus, an apodemal arm projects posteriorly from the suture delimiting the subalare from the metepimeron.

STERNUM: The entire ventral surface of an insect's body is the "venter". The whole ventral surface of a thoracic segment is the "sternum". A subdivision of the sternum is a "sternite". Audouin (1824) regarded the sternum as a single plate. MacLeay (I830) proposed that each thoracic segment comprises four subsegments or annuli, represented in the sternum by the "praesternum", "sternum", "sternellum" - 39 - i and "poststernellum". Crampton (1909) unfavourably criticised MacLeay ' s terminology and gave three reasons for re- jecting it:-

1. He contended that MacLeay has not figured or described these regions. Furthermore, he believed that MacLeay has not seen these regions in any insect, but merely inferred their existence from the condition of the tergum.

2, The application of the designation "sternum" to the whole ventral region of the segment prohibits its use for a subdivision of that region.

3- The use of these terms implies a non-existent relation between the subdivisions of the sternum and those of the tergum, for these subdivisions never exist as annuli,

Crampton (op.cit.) adopted', however, the term "presternum" in the sense in which it has been used by Comstock & Kochi (1902). For the remaining subdivisions of the sternum he introduced the terms "basisternum", "furcasternum", "postfurcasternum" and "spinasternum". Crampton regarded his terms as original designations for parts which have never been described before and did not consider them as synonymous with those of MacLeay. Snodgrass (1927), although he made no mention of MacLeay, has applied MacLeay' s terminology to the sternal region. Later, Snodgrass (1935) suggested his own terms for some of the sternal plates but he applied these terms in various senses. Table (1) gives a summary of the different appellations used by Snodgrass compared with those of MacLeay/and Crampton. When examining - 40 - i the table, the following points should be taken into account:-

1. Despite Crampton's claim that his terms do not correspond to those of MacLeay it is assumed that MacLeay's terms are synonymous with those of Crampton.

2. Minor spelling variations have been neglected and all the terms have been written as they are spelt now.

According to Snodgrass (1927, 1952), Crampton's terminology is not satisfactory because the basisternum is not always basal and the sternal apophyseal arms of the generalised insects are widely separated and do not form a furca. The objections Snodgrass raised against the usage of the terms basisternum and furcasternum do not justify the rejection of these terms and his usage of some of his own terms is indefinite, e.g. the "eusternum", antesternum" and "poststernum". Moreover, most ..entomologists still refer to the sternal apophyses as the furca or furcal arms even when their bases are widely separated. In the present account, Crampton's terminology of the sternal plates is adopted, because it is simple and reasonably descriptive of the various sclerites.

The components of the thoracic sternum as traditionally conceived are the "presternum", "basisternum","furcasternum (=sternellum) and "spinasternum". These sclerites may exist as distinct plates in the prothorax of the Diptera and can be recognised throughout the thorax of more generalised insects but they are greatly modified in the I - 41 - pterothoracic segments of the Diptera.

The prothoracic presternum was alluded to in the discussion of the cervical sclerites.

The prothoracic basisternum, or the "probasisternum" is the sclerite that lies between, and a little anterior to, the fore coxae. Systematists refer to it as the "prosternum". A serious morphological objection to this usage is that the designation prosternum should be applied to the whole sternal region of the prothorax and therefore should not be applied to one of its subdivisions. Speight (1969) followed this erroneous application, arguing that the other components of the prosternum are of little significance. In Tipula Rees & Ferris (1939) designated both the basisternum and furcasternum as the prosternum. Later, Ferris (1940a) reinterpreted the anterior part of this sclerite as a portion of the subcoxal arcs. In his study of Drosophila, Ferris (1950) considered the sclerite separating the fore coxae as part of the preepisternum. He used the presence on this plate of a longitudinal furrow as evidence in support of his claim, apparently assuming that the sternal sclerites could not be divided into two longitudinal parts since they originate from the median ventral area. Ferris's concept of the sternum is rather surprising, he put forth the opinion that the basisternum, when present, is either secondarily developed or is formed by a forward expansion of the furcasternum. Sara & Smerdel (1953)» presumably influenced by Ferris, designated the probasisternum as the precoxale in Asilus. - 42 - i

The most detailed study of the probasisternum is that by Speight (1969), who examined this organ in 23 families of Acalypterae. He found a great deal of variation in its shape and size. This character could, however, be used in locating misplaced species and in defining genera as well as in showing the affinities of some groups.

The basisternum is variable in both shape and relative size in the different families of Brachycera. Most families include genera in which the probasisternum is united to the proepisternum. Medially, the basisternum is partly or completely divided by a longitudinal farrow, the "basisternal suture". Internally, this suture usually bears a ridge or "carina" that may be well developed or may be very weak. In some stratiomyids, the longitudinal basisternal suture is obsolete and the carina lacking.

The profurcasternum lies behind the basisternum and is separated from it by a costosternal suture. According to Snodgrass (1935). this suture extends transversely between the bases of the profurcal pits. Bonhag (1949) recognises two sutures in this region of Tabanus, the anterior one he termed the costosternal suture. He considers the posterior suture that extends transversely between the furcal pits to be a secondary development. The furcasternum is thus divided into an anterior portion which in some groups is bent inwards, so that its surface forms an angle with the basisternum, and a posterior portion lying between the arms of Y-shaped lines extending posteriorly, and so limiting the furcasternum from the proepimeral - 43 - i sclerites. Internally, these lines may bear strongly developed ridges which fuse with the median mesosternal ridge posteriorly and with the profurcal arms anterolateral^. There are groups in which the lateral boundaries of the fureasternum are only faintly defined and the internal ridges lacking.

The lateral angles of the furcasternum bear the profurcal pits which invaginate internally to give rise to the furcal arms. These arms extend dorsally to unite with the corresponding pleural apophyses. Generally, the prothoracic furcal pits are well separated from each other but in Toxophora they are closely approximated and in Systropus the two pits become confluent and lie on the mid ventral line. This modification is not influenced by an approxi- mation of the procoxae. The common furcal base gives rise to the median furca that extends a short distance before forking into two lateral arms. Each arm then uniteswith the pleural apophysis extending dorsal to it.

In the present work, a distinct spinasternum is recognised in the prothorax of Systropus. This seems to be the first report of this sclerite in the Diptera. The spina- sternal pit is situated on the median ventral suture, a short distance behind the greatly reduced posterior part of the furcasternum. The pit is embraced by the short arms of a posteriorly directed transverse suture. Intern- ally, the pit invaginates to give rise to the spina that terminates in two lateral spinal arms. Each arm extends anterodorsally to unite with the corresponding furcal arm in front of it. - 44 - ,

In the pterothoracic segments of the higher Diptera the morphological composition of the ventral region is far from clear. In regard to the views concerning the topo- graphy of the plates separating the fore pair of legs from the middle and those from the hind pair, there is little disagreement. Young (1921) gave a very accurate picture of the situation when he stated: "The study of the venter of flies is carried with difficulty because of the proxi- mity of the bases of the legs . But a number of the broader representatives of the group show the same arrangement of sclerites as does Olfersia americana (Hippoboscidae), in which the two pleurites termed sternopleurites (=preepi- sterna of Ferris) meet each other on the ventral side apparently crowding out the anterior part of the sternum (=mesobasisternum). Crampton (1942) admits the possibility of the mesobasisternum becoming inrolled between the two flanks of the sternopleurites as these extend downward towards the mid-ventral line. Snodgrass (1952) states that in the mesothorax, the episternal plate extends- veritrally in- to the sternal region. But how far this extension occurs, he leaves undecided. Matsuda (1970), adopting a line very similar to that of Snodgrass, claims that an undefinable basisternal area may be present on both sides of the median ventral suture. Ferris (1940b) asserts that the preepisternal plates extend ventrally to meet each other along the mid-ventral line,thus forming a "discrimen" or "discriminal line". Ferris did not deny the possibility of the presence of sternal elements near the apex of the mid-ventral line, but did not accept that they could be visible externally. - 45 - i

The difference between his view and that of Snodgrass and Matsuda appears, in the Diptera, to be one of degree rather than kind.

The middle coxae are separated by two narrow cuticular bands which appear to be continuous with the preepisternal areas in front and the meral regions behind them. The lateral margins of these "bands are expanded mesally to form the ventral coxal condyles . The median ventral suture separating the two bands is interrupted by the confluent mesofurcal pits. Crampton (1942) considers these narrow bands to be the furcasternum and regards the ventral coxal condyles as parts of them. Snodgrass (1935) suggests two possible explanations for the apparent continuity of these bands with the lateral pleural sclerites:-

1. The sternum may be "bordered by very narrow subcoxal plates that carry the coxal condyles and complete the subcoxal rings about the coxae.

2. The ventral coxal articulations may be secondary developments originating from the sternum.

Ferris & Rees (1939) contend that the ventral coxal condyles are primitive structures derived from the subcoxal arcs and cannot originate from the sternum. Basing his argument on the preconception that the furcal pits of the pterothoracic segments are, primitively, set close together on the median ventral line, Ferris (1940b) states forcibly: "The apophyseal pits are invaginations not between the primitive subcoxae and the sternite (as Weber., 1928, has - 46 - i

suggested) but between the primitive subcoxae". He thus denies the involvement of any external sternal elements between the coxae. Bonhag (194-9) adopts similar views.

Basically, the ventral area in the metathorax conforms to the same ground plan as in the mesothorax and further consideration here would be redundant. - 47 - i

TABLE (l) : Terminology of the Insect Sternum

MacLeay Pre- Sternum Sterne Hum Poststernellum (1830) sternum

Crampton Pre - Basi- Furca- Postfurca- Spina- (1909) sternum sternum sternum sternum sternum

Snodgrass St ernum Prop er (1927) Sternum Sternellum Poststermu m Pre- sternum Basi- Furca- Postfurca- Spina- sternum sternum sternum sternum

Snodgrass Eusternum (1935) Pre- Basi- Sternellun . Spina- sternum sternum sternum

Snodgrass Sternum Sternellum , (1952) Eusternum Spina- sternum Basisternum Furca- sternum Antesternum

P oststernum - 48 - i

IV MORPHOLOGY OF THE THORAX

In this section an account is given of the thoraces of 19 species from 19 families of Brachycera. (Systropus edwardsi (Bombyliidae) is included in the character summary table because of the many peculiarities it demonstrates). The species described are:-

1. Atylotus agrestis 11. Systropus edwardsi 2. Pelecorhynchus fusconiger 12. Ogcodes gibbosus 3. Panophthalmus tabaninus 13. Prosoeca accincta 4. Chorisops tibialis 14. Ectyphus pinguis 5. Xylomya tenthredinoides 15. Scenopinus fenestralis 6. Xylophagus fulgidus 16. Psilocephala sequa 7. Coenomyia ferruginea 17. Apiocera trimaculata 8. Rhagio scolopaceus 18. Machimus atricapillus 9. Hilarimorpha sidora 19. Empis livida 10. Exhyalanthrax lugens 20. Poecilobothrus nobilitatus

The thoracic structures of Atylotus agrestis are described in detail and all illustrations of this species are fully labelled. For the remaining species, only characters that demonstrate more than one state of expressions are mentioned. Constant features that occur repeatedly in all species are omitted, and only sufficient structures noted to emphasise homologies.

The prephragma is bilaterally asymmetrical about the median dorsal line. Two forms of distortion occur: a structural and orientational one. Only the former is shown on the figures.

The prefixes pro-, meso- and meta- (and the corresponding arable numerals 1, 2, 3 suffixed to lettering on illustrations) are used for designating structures of the prothorax, mesothorax and metathorax, respectively.

Information obtained during this investigation on the nature of different structures is summarised in Table 2. - 49 - i

1. Atylotus agrestis (figs. 1-4, 6)

CERVIX: The dorsocervicalia are absent. The anterocervicalia (ac) extend alongside the upper margins of the laterocervicalia (lc), which form the principal cervical plates. These have subconical, strongly convex bases and their anterior processes are short and broad. The postcervicalia (pc) lie transversely behind the bases of the laterocervicalia. The sella (se), which occupies the ventral area between the bases of the laterocervicalia, bears two loose bundles of sensilla anteriorly. A medial impression divides it into an anterior sensilla-bearing part and a posterior section. It is not tapering posteriorly. The corniculae (co) extend transversely anterior to the sella.

PROTHORAX: The antepronotum ( an^) consists of a narrow mid- dorsal collar and a lateral area, on each side, in which the ventral part is rounded and conspicuously swollen. The proepisternum (es^) is separated from the probasisternum (bs^) by membrane. The proepimeron (em^) is delimited from the mesanepisternum (aes2) by the mesanepisternal suture (aess2) and from the profurcasternum (fs^) by the sternopleural suture (spls^). The probasisternum is completely divided by the longitudinal basisternal suture (bss^) which marks the course of a weak internal carina (bsca-j). The costosternal suture (cs^) that separates the basisternum from the furcasternum is prominent. The latter sclerite is divided by a transverse suture (vts^), which is the manifestation of an internal ridge (vtr^) connecting the bases of the profurcal arms (fa-j). These arise from the invaginated furcal pits (fpt.j) and extend dorsally to unite with the propleural apophyses (pla^). Each furcal arm bears an anteromedially directed spur (fp^) in the middle. The pleural apophyses continue dorsally into the transnotal ridges (tr-j) which attain the lateral margins of the prephragma (aph).

MESOTHORAX: The prephragma is well developed and strongly bilobed. Its lateral arms are approximated distally. - 50 - i

Laterally, it continues both with the transnotal ridge and postpronotal ridge (pnr^). The subtriangular mesoprescutum (psc2) extends lateral to the mesoscutum (sc2), on each side, to end before the wing base. Its posterior margin continues ventrally as the prealar arm (npla2). The prescutum is separated from the scutum by the prescutoscutal suture (pscs2). The internal ridge (pscr2) arising from this suture is provided with an anterior arm (apsca2) and a posterior arm (ppsca2). The mesoscutum is divided into three longitudinal regions by two dorsolateral sutures (dls2). Each lateral area is traversed by an anterior trans-scutal suture (ats2) and a posterior trans-scutal suture (pts2) . The lateral margins of the scutum are callose, forming lobate structures. The most prominent of these are a lobe in front of the anterior trans-scutal suture and one immediately behind it. The prescutoscutal suture continues posteriorly into the lateral me.soscutal suture (lscs2>. This sets off the shelf-like suralar plate (sur2) that provides the robust, notched anterior notal wing process (anwp2). The elevated area behind the suralare is traversed by a narrow tergal fissure

(tgf2). The anterodorsal margin of the fissure bears a well developed, hook-like apodeme internally (tga2). The depressed lateral margin extending behind the tergal fissure forms the median notal wing process (mnwp2). The trans-scutellar suture is represented by a deep impression (tscls2) that divides the scutellum into an anterior and posterior part.

The evaginated part of the scutellum (scl2) is greatly developed; it overgrows the postnotum to reach the anterior margin of the abdomen. On each side of the elevated part of the scutellum, there is an anterior and posterior ridge. The anterior ridge forms a bridge with the scutum. The posterior ridge forks into an anterior arm that forms the folded posterior notal wing process (pnwp2) and a posterior arm that continues into the axillary cord (axc2). The postnotum is divided by two lateral sutures into a mediotergite (mt2) and a laterotergite (lt2) on each side. The posterior margin of the mediotergite continues into the postphragma (pph). The laterotergites are conspicuously swollen and their anterior - 51 - i

margins bound by sutures. The base of the postphragma turns forwards to unite with the anteroventral edges of the ridges arising from beneath these sutures. The mesopleuron is divided by the tortuous mesopleural suture (PIS2) into the anterior mesepisternum and posterior mesepimeron. The subhorizontal portion of this suture is long and the mesepisternum intrudes into the mesepimeral region. The anepisternal suture completely divides the mesepisternum into the dorsal anepisternum and ventral preepisternum (pes^). The mesospiracle (SP2) is embedded in a membranous cleft that continues posteriorly into the notopleural cleft (nplc2) delimiting the anepisternum from the prescutum. The bipartite basalare (ba2) is separated from the posterodorsal apex of the anepisternum by a suture that extends ventrally to set off a narrow marginal area from the rest of the anepisternum. Internally the basalare bears a well developed apodeme (baa2) arising from the common wall joining the two parts of this plate. The transverse basalar cleft (bac2) delimits the pleural wing process (PIWP2) from the anepisternal region. The subalare (sb2) lies half detached in the soft cuticle between the mesanepimeron (aem2) and the wing base. The mesepimeron is divided by the anepimeral suture (aems2) into the dorsal anepimeron and ventral katepimeron (ken^). The latter is indistinguishably fused with the mesomeron (n^). The confluent mesofurcal pits (fpt2) lie on the mid-ventral line between the wing-like flaps that form the ventral coxal processes or condyles (VP2). Internally the pits invaginate to form the mesofurca which terminates in the two furcal arms (fa2) bearing the paired furcal cups (afc2* pfc2). The longitudinal median ridge (lm^) supporting the mesofurcal arms extends anteriorly to the posterior apex of the profurcasternum.

METATHORAX: The metanotum is reduced to two narrow bands which, dorsally, are overlapped by the first abdominal tergite. These are the metascutum (an^), which connects the halteres (hi), and the metapostnotum (pn^), which is laterally continuous with the metepimeron (em^) behind the halteres. - 52 - i

The metanepisternum (aes^) is reduced as a result of the intrusion caudally of the mesomeron. The confluent metafurcal pits (fpt^) invaginate to form the short metafurca, which terminates in two metafurcal arms (fa^). These are flat and extend laterally to abut on the corresponding ventral pleural arms (vpla©.

2. Pelecorhynchus fusconiger (figs. 7, 9a, 10a)

CERVIX: Dorsocervicalia (dc) short and broad. Latero- cervicalia with subconical, slightly convex bases; their anterior processes short and broad. Sella bears two loose bundles of sensilla. It is broad posteriorly.

PROTHORAX: Mid-dorsal collar of antepronotum narrow; lateral areas broad and slightly swollen. Postpronotal lobes much reduced, slightly elevated and their posterior margins weakly truncate. Proepisternum separated from probasisternum by membrane. Proepimeron indistinguishably fused to mesepisternum. An isolated suture partly divides it into a dorsal and ventral part. Probasisternum completely divided by probasisternal suture. Basisternal carina weak. Costo- sternal suture present. Ventral transverse suture present. Sternopleural. sutures present.

MESOTHORAX: Prephragma well developed; strongly bilobed; lateral arms approximated distally. Mesoprescutum strap- like; narrow. Dorsolateral sutures present. Anterior and posterior trans-scutal sutures present. Tergal apodeme well developed. Trans-scutellar suture represented by a shallow impression. Evaginated part of suctellum medium-sized. Mediotergite medium-sized; delimited by lateral sutures. Laterotergites almost flat. Mesospiracle embedded in wide membrane. Mesanepisternal suture complete. Mesopleural suture angularly bent; its subhorizontal portion long.. - 53 - i

Mesomeral fissure present. Mesomeron intrudes slightly into metapleural region.

METATHORAX: Metanotum not remarkable. Metafurca terminates in two furcal arms. Each arm branches into a tiny anterior limb and a broad posterior limb.

3. Pantophthalmus tabaninus (figs. 8, 9b, 10b)

CERVIX: Dorsocervicalia absent. Laterocervicalia with subconical, strongly convex bases; their anterior processes short and broad. Sella bears two loose bundles of sensilla. It is greatly prolonged posteriorly but not tapering.

PROTHORAX: Mid-dorsal collar of antepronotum narrow; lateral areas broad and slightly swollen. Postpronotal lobes much reduced, slightly elevated and their posterior margins weakly truncate. Proepisternum narrowly united to probasisternum. Proepimeron indistinguishably fused to mesepisternum. An isolated suture partly divides it into a dorsal and ventral part. Probasisternum completely divided by probasisternal suture. Basisternal carina weak, Costosternal suture present. Ventral transverse suture present. Sternopleural sutures obliterated anteriorly.

MESOTHORAX: Prephragma well developed; strongly bilobed. Mesoprescutum strap-like; narrow. Anterior and posterior trans-scutal sutures present. Tergal apodeme medium-sized. Trans-scutellar suture represented by a shallow impression. Evaginated part of scutellum medium-sized. Mediotergite reduced, delimited by lateral sutures. Laterotergites large; almost flat. Mesospiracle embedded in wide membrane. Mesanepisternal suture lost anteriorly. Meso- pleural suture angularly bent; subhorizontal portion long. Mesomeral fissure absent. Mesomeron intrudes slightly into the metapleural region. \ - 54 - i

METATHORAX: Metanotum not remarkable. Metafurca termin ates in two furcal arms. Each arm branches into a tiny anterior limb and a broad posterior limb.

4. Chorisops tibialis (figs. 11-13, 16a).

CERVIX: Dorsocervicalia short and broad. Laterocervicalia with subconical, strongly convex bases; their anterior processes slightly elongate and narrow. Sella bears two loose bundles of sensilla. It is weakly constricted medially; not tapering posteriorly.

PROTHORAX: Mid-dorsal collar of antepronotum broad; lateral areas broad and slightly swollen. Postpronotal lobes elevated and their posterior margins smooth. Proepister- num broadly united to probasisternum. Proepimeron indistinguishably fused to mesepisternum. Probasisternum partly divided by the reduced probasisternal suture. Basis- ternal carina weak. Costosternal suture poorly defined. Ventral transverse suture absent. Sternopleural sutures absent.

MESOTHORAX: Prephragma well developed; strongly bilobed. Mesoprescutum strap-like; narrow. Anterior and posterior, trans-scutal sutures present. Tergal apodeme well developed. Trans-scutellar suture represented by a shallow impression. Evaginated part of scutellum large; its posterior margin bears four strong spines (sclp2). Anterior part of mediotergite differentiated into a strongly convex subscutellum (SSCI2)• Mediotergite delimited by lateral sutures. Laterotergites slightly callose. Mesospiracle borne on the anterodorsal apex of the mesanepisternum. Mesanepi-

sternal suture lost anteriorly. Mesanepisternal pad (aesp2) present. Mesopleural suture angularly bent; its subhorizontal portion relatively long. Mesomeral fissure absent. Mesomeron intrudes slightly into metapleuron. - 55 - i

METATHORAX: Metanotum not remarkable. Metanepisternum reduced as a result of the intrusion caudally of the mesomeron. Metafurca terminates in two concave, wing-like furcal arms. Each arm branches into an anterior and posterior limb.

5. Xylomya tenthredinoides (figs. 18a, 19b, 20b)

CERVIX: Dorsocervicalia short and broad. Laterocervicalia with subconical, strongly convex bases; their anterior processes slightly elongate and narrow. Sella carries two loose bundles of sensilla. It is weakly constricted medially; not tapered posteriorly.

PROTHORAX: Mid-dorsal collar of ..antepronotum broad; lateral areas broad and slightly swollen. Postpronotal lobes large; conspicuously swollen and their posterior margins smooth. Proepisternum broadly united to probasisternum. Proepimeron indistinguishably fused to mesepisternum but the sternopleural suture, which is lost anteriorly, partly separates it from the profurcasternum. Pro- basisternum completely divided by the longitudinal basisternal suture. Probasisternal carina very weak. Costo- sternal suture present. Ventral transverse suture poorly defined.

MESOTHORAX: Prephragma well developed; strongly bilobed. Mesoprescutum strap-like and narrow. Anterior and posterior mesothoracic trans-scutal sutures present. Tergal apodeme medium-sized. Trans-scutellar suture represented by a shallow impression. Evaginated part of scutellum short. Subscutellum weakly convex. Mediotergite large; delimited by lateral sutures. Laterotergites large; almost flat. Mesospiracle lies at the anterodorsal apex of the mesanepisternum. Mesanepisternal suture lost anteriorly. Mes- anepisternal pad present. Mesopleural suture softly bent; - 56 - i

its subhorizontal portion short. Mesomeral fissure present. Mesomeron intrudes slightly into the metapleural area.

METATHORAX: Metanotum not remarkable. Metanepisternum slightly reduced as a result of the intrusion caudally of mesomeron. Metafurca terminates in two concave, wing-like arms. Each arm branches into an anterior and posterior limb.

6. Xylophagus fulgidus (figs. 18b, 19a, 20a)

CERVIX: Dorsocervicalia absent. Laterocervicalia with subconical, strongly convex bases; their anterior processes slightly elongate and narrow. Sella carries two loose bundles of sensilla. It is weakly constricted medially; not tapered posteriorly.

PROTHORAX: Mid-dorsal collar of antepronotum broad; lateral areas broad and slightly swollen. Postpronotal lobes large; slightly elevated and their posterior margins smooth. Proepisternum separated from probasisternum by sunken membrane. Proepimeron indistinguishably fused to the mesepisternum but the sternopleural suture separates it from the profurcasternum. Probasisternum completely divided by the longitudinal basisternal suture. Probasi- sternal carina weak. Costosternal suture prominent. Ven- tral transverse suture lacking.

MESOTHORAX: Prephragma well developed; strongly bilobed. Mesoprescutum strap-like and narrow. Anterior and posterior mesothoracic trans-scutal sutures present. Dorso- lateral mesoscutal sutures present. Tergal apodeme well developed. Trans-scutellar suture represented by a shallow impression. Evaginated part of scutellum short. Sub- scutellum weakly convex. Mediotergite large; delimited by » - 57 -

lateral sutures. Laterotergites large; almost flat. Mesospiracle embedded in membrane. Mesanepisternal suture lost anteriorly. Mesopleural suture angularly bent; its subhorizontal portion short. Mesomeral fissure present. Mesomeron intrudes slightly into the metapleural area.

METATHORAX: Metanotum not remarkable. Metanepisternum slightly reduced as a result of the intrusion caudally of mesomeron. Metafurca terminates in two concave, wing-like furcal arms. Each arm branches into an anterior and posterior limb.

7. Coenomyia ferruginea (figs. 21, 22)

CERVIX: Dorsocervicalia absent. Laterocervicalia with subconical, slightly convex bases; their anterior processes short and broad. Sella bears two loose bundles of sensilla. It is weakly constricted medially; not tapering posteriorly.

PROTHORAX: Mid-dorsal collar of antepronotum broad; lateral areas as broad as collar; slightly swollen. Post- pronotal lobes reduced; slightly elevated and their posterior margins weakly truncate. Proepisternum not continuous with probasisternum. The latter expands laterally, on each side, ana terminates in a narrow, finger-like process that does not attain the proepisternum. Probasi- sternum completely divided by probasisternal suture. Probasisternal carina of moderate size. Costosternal suture present. Ventral transverse suture present. Ster- nopleural sutures present,

MESOTHORAX: Prephragma well developed; strongly bilobed; lateral arms approximated distally. Mesoprescutum strap- like; narrow. Anterior trans-scutal suture absent. - 58 - i

Posterior trans-scutal suture present. Tergal apodeme medium-sized. Trans-scutellar suture represented by a deep impression. Evaginated part of scutellum short; its posterior margin bears two strong spines. Mediotergite medium-sized; delimited by lateral sutures. Latero- tergites large; conspicuously callose. Mesospiracle borne on the anterodorsal apex of the mesanepisternum. Mesanepisternal suture lost anteriorly. Mesopleural suture angularly bent; its sub-horizontal portion short. Mesomeron slightly intruding into metapleuron.

METATHORAX: Metanotum not remarkable. Metanepisternum slightly reduced as a result of the intrusion caudally of the mesomeron. Metafurca terminates in two concave, wing- like arms. Each arm branches into an anterior and posterior limb.

8. Rhagio scolopaceus (fgis. 23, 26a, 27a)

CERVIX: Dorsocervicalia absent. Laterocervicalia with subconical, strongly convex bases; their anterior processes slightly elongate and narrow. Sella bears two loose bundles of sensilla; not constricted medially; not tapering posteriorly. A cuticular thread connects it to the probasisternum.

PROTHORAX: Mid-dorsal collar of antepronotum narrow; lateral areas subquadrangular, nearly flat. Postpronotal lobes slightly elevated and their posterior margins truncate. Proepisternum separated from probasisternum by membrane. Proepimeron partly delimited from mesepisternum by the ventral part of the mesospiracular cleft and the sternopleural suture marks the boundary between it and the profurcasternum. Probasisternum completely divided by probasisternal suture. Probasisternal carina weak. Costo sternal suture present. Ventral transverse suture present. - 59 - i

MESOTHORAX: Prephragma well developed and strongly bilobed; lateral arms approximated distally. Mesoprescutum subtriangular; tapering posterirly. Longitudinal dorsolateral mesoscutal sutures present. Anterior and posterior trans-scutal sutures present. Tergal apodeme well developed. Trans-scutellar suture represented by a deep impression. Evaginated part of the scutellar plate of medium size. Mediotergite delimited by lateral sutures. Latero- tergites slightly callose. Mesospiracle embedded in wide membrane. Mesanepisternal suture lost anteriorly. Meso- pleural suture softy bent; its subhorizontal portion very short. Mesomeral fissure present. Mesomeron not intruding into metapleural area.

METATHORAX: Nothing remarkable about the metanotum. A short suture arises from the ventral part of the posterior intersegmental suture and extends posteroventrally to merge into the metanepisternal suture, thus setting off a small triangular area from the metanepisternum. Metafurca terminates in two concave, wing-like furcal arms. Each arm branches into an anterior and posterior limb.

9. Hilarimorpha sidora (figs. 25a, 28)

CERVIX: Dorsocervicalia short and broad. Laterocervicalia with subconical, strongly convex bases; their anterior processes short and broad." Sella bears two compact bundles of sensilla. It tapers posteriorly, without forming a long median bar.

PROTHORAX: Mid-dorsal collar of antepronotum relatively broad; lateral areas narrow and slightly swollen. Post- pronotal lobes swollen and their posterior margins smooth. Proepisternum separated from probasisternum by membrane. Proepimeron partly separated from mesepisternum by the - 60 - i

ventral portion of the anterior intersegmental suture. Ven- trally, a weak sternopleural suture delimits it from the profurcasternum. Probasisternum completely divided by probasisternal suture. Basisternal carina weak. Costo- sternal suture prominent. Ventral transverse suture present.

MES0TH0RAX: Prephragma well developed and strongly bilobed. Mesoprescutum subtriangular; tapering posteriorly. Ant- erior trans-scutal suture reduced. Posterior trans-scutal suture present. Tergal apodeme much reduced. Trans- scutellar suture represented by shallow impression. Evag- inated part of scutellum short. Mediotergite delimited by lateral sutures. Laterotergites almost flat. Mesospiracle embedded in wide membrane. Mesanepisternal suture lost anteriorly. Mesopleural suture softly bent; its subhorizontal portion very short. Mesomeral fissure present. Mesomeron not intruding into metapleural area.

METATHORAX: Metanotum not remarkable. Posterior intersegmental suture softly bent. Metafurca terminates in two furcal arms. Each arm branches into a long anterior limb and a very short posterior limb.

Exhyalanthrax lugens (figs. 29, 30, 32a, 36a, 37b)

CERVIX: Dorsocervicalia elongate and narrow. Latero- cervicalia with subquadrangular flat bases; their anterior processes greatly elongate and narrow. Postcervicalia extend longitudinally and their mesal edges abut on the posterior margins of the laterocervicalia. The sella appears as though it has been forcibly pulled forwards, so forming a spear-shaped structure. The corniculae are likewise displaced forwards and inwards, thus producing a sheath surround ing the protracted sensillar plates. A sclerotised median - 61 - i

bar connects the sella with a thick, shiny membranous flap (mf) that occupies the ventral cervical area between the sella and occiput. Posteriorly, the sella continues as a sclerotised median bar connected to the probasisternum by a thin cuticular thread.

PROTHORAX: Mid-dorsal collar of antepronotum greatly expanded anteriorly; lateral areas elongate and slightly swollen. Transnotal suture interrupted by a median break. Postpronotal lobes elevated and their posterior margins truncate. The ventral edge of the proepisternum fades into an area which could either be described as poorly sclerotised plate or pigmented membrane. The lateral edges of the probasisternum are also poorly defined. Proepimeron partly separated from mesepimeron by an isolated suture, which probably is a remnant of the ventral part of the anterior intersegmental suture. Probasisternum completely divided by probasisternal suture. Costosternal suture present. Ventral transverse suture absent. Sternopleural sutures present.

MESOTHORAX: Prephragma greatly reduced; represented by a thin, narrow cuticular plate that lacks the lateral arms. Mesoprescutum subtriangular, tapering posteriorly. Anter- ior trans-scutal suture obliterated. Posterior trans-scutal suture present. Tergal apodeme well developed. It arises from beneath a wedge-shaped sclerite (tgfl) which is well differentiated from the surrounding area. Trans-scutellar suture represented by a deep impression. Evaginated part of scutellum well developed. Mediotergite greatly reduced; not delimited by lateral sutures. Laterotergites conspicuously callose. Mesospiracle embedded in a membranous cleft, which is separated from the notopleural cleft by a weakly cuticular bridge connecting the mesanepisternum to the posterior margin of the postpronotum. The edges of the mesospiracular cleft approach each other ventrally, producing a secondary suture that partly separates the mesepisternum from the proepimeron. Mesanepisternal suture lost anteriorly. I - 62 -

Mesopleural suture angularly bent; subhorizontal portion relatively long. Mesomeral fissure present. Mesomeron not intruding into metapleural area.

ME3TATH0RAX: Metanotum not remarkable. Posterior intersegmental suture softly bent. Metafurca branches into two furcal arms. Each arm terminates in a convex, club-shaped head.

11. Systropus edwardsi (figs. 31, 34b, 37a)

(see table of characters)

12. Ogcodes gibbosus (figs. 40, 41, 43a)

CERVIX: Dorsocervicalia absent. Laterocervicalia with subconical, strongly convex bases; anterior processes short and broad. Sella bears two compact bundles of sensilla. It is tapered posteriorly without forming a median bar.

PROTHORAX: Mid-dorsal collar of antepronotum narrow; lateral areas narrow. Postpronotal lobes large; almost flat; their posterior margins weakly truncate. Proepi- sternum reduced to a very narrow rim; united to the probasisternum by a strap-like, narrow cuticular bridge. Proepi- meron indistinguishably fused to mesepisternum. Probasi- sternum completely divided by probasisternal suture. Costosternal suture present. Ventral transverse suture obliterated. Sternopleura}. sutures weakly distinct.

MESOTHORAX: Prephragma well developed; base very broad; tapers into a single median arm. Mesoprescutum very narrow anteriorly, becoming broader posteriorly. Anterior - 63 - i

and posterior trans-scutal sutures absent. Tergal apodeme much reduced. Trans-scutellar suture represented by a shallow impression. Laterotergites greatly reduced; weakly callose. Mesospiracle borne on the anterodorsal apex of the mesanepisternum. Mesanepisternal suture lost anteriorly. Two depressed lines diverge from the anterior extremity of suture; one extends obliquely to near the ventral edge of the mesospiracle, while the other extends anteriorly to reach the propoleural suture. Mesopleural suture very softly bent; practically no subhorizontal portion. Mesomeral fissure represented by a rounded membranous area near the mesopleural suture. Mesomeron not intruding into metapleural region.

METATHORAX: Metanoturn not remarkable. Metafurca terminates in two unbranched furcal arms. Each arm bears a short, cup-shaped stump on the outer side.

Prosoeca acoincta (figs. 44, 45a, 46c, 56a)

CERVIX: Dorsocervicalia short and broad. .Lateroservicalia with subconical, strongly convex bases; anterior processes short and broad. Sella bears two compact bundles of sensilla. It is weakly constricted medially; short, not tapered posteriorly.

PROTHORAX: Mid-dorsal collar of antepronotum narrow; lateral areas narrow and conspicuously swollen. Postpronotal lobes much reduced in size, almost flat and their posterior margins weakly truncate. Proepisternum strap-like and narrow; separated from probasisternum by membrane. Proepi- meron separated from mesepisternum by suture. Probasisternum completely divided by probasisternal suture. Costosternal suture present. Ventral transverse suture present. Sterno- pleural sutures present. - 64 - i

MESOTHORAX: Prephragma medium-sized; tapers distally into a single median arm. Mesoprescutum strap-like; narrow. Dorsolateral sutures present, anterior and posterior trans- scutal sutures present. Tergal apodeme much reduced. Just behind the tergal fissure, at the base of the posterior trans- scutal suture, there is, on each side, a small tubercle (tgtb). Trans-scutellar suture absent. Evaginated part of scutellum short. Mediotergite medium-sized; delimited by lateral sutures. : Laterotergites medium-sized; slightly callose. Mesospiracle embedded in membrane. Anterodorsal apex of mesanepisternum extends towards the posterior margin of the postpronotum. Mesanepisternal suture lost anteriorly. Mesopleural suture angularly "bent; subhorizontal portion long. Mesomeral fissure absent. Mesomeron intrudes slightly into metapleural area.

METATHORAX: Metanotum not remarkable. Metafurca terminates in two unbranched, broad furcal arms.

Ectyphus pinguis (figs. 47, 49a, 56b)

CERVIX: Dorsocervicalia absent. Laterocervicalia with subquadrangular, almost flat bases; anterior processes slightly elongate and narrow. Sella bears two compact bundles of sensilla. It is tapered posteriorly; not produced into a narrow median bar.

PROTHORAX: Mid-dorsal collar of . antepronotum broad; lateral areas much reduced as a result of the expansion dorsally of the proepisternum. Postpronotal lobes elevated and their posterior margins truncate. Proepisternum broadly united to probasisternum. Proepimeron partly divided by a suture into an anterior and posterior part. The latter is further divided by an isolated suture into a dorsal and ventral portion. . Posteriorly the proepimeron and mesepisternum are united without a suture. Probasisternum - 65 - i

incompletely divided by probasisternal. suture. Costosternal suture present. Ventral transverse suture present. Sterno- pleural sutures present.

MESOTHORAX: Prephragma greatly reduced; weakly indented distally. It extends from a broad plate formed as a result of the fusion of the two transnotal ridges along the median dorsal line. Mesoprescutum strap-like; narrow. Anterior and posterior trans-scutal sutures absent. Tergal apodeme apparently absent. Trans-scutellar suture represented by a shallow impression. Evaginated part of scutellum much reduced. Mediotergite medium-sized; not delimited by lateral sutures. Laterotergites greatly reduced in size; conspicuously swollen. Mesospiracle embedded in membrane. Mesanepisternal suture lost anteriorly. Mesopleural suture softly bent; subhorizontal portion very short. Mesomeral fissure absent. Mesomeron not intruding into the metapleural area.

METATHORAX: Metanotum not remarkable. Metafurca terminates in two concave, wing-like arms. Each arm branches into an anterior and posterior limb.

Scenopinus fenestralis (figs. 50, 51)

CERVIX: Dorsocervicalia elongate and narrow. Laterocer- vicalia with subconical, strongly convex bases and their anterior processes elongate and narrow. Sella carries two compact bundles of sensilla. It is tapered posteriorly but not forming a median bar.

PROTHORAX: Mid-dorsal collar of antepronotum narrow and evanescent in the median dorsal line. Lateral areas oval and slightly swollen. Postpronotal lobes large and almost flat, and their posterior margins smooth. Proepisternum - 66 - i

broadly united to Probasisternum. Proepimeron indistinguishably fused to mesepisternum and profurcasternum. Pro- basisternum partly divided by the reduced probasisternal suture. Probasisternal carina weak. Costosternal suture poorly defined. Ventral transverse suture absent.

MESOTHORAXt Prephragma well developed and strongly bilobed. Mesoprescutum strap-like and narrow. Anterior trans- scutal suture obliterated. Posterior trans-scutal suture present. Tergal apodeme reduced. Trans-scutellar suture represented by a shallow impression. Evaginated part of scutellum short. Mediotergite not delimited by lateral sutures. Laterotergites shifted anteriorly, much reduced in size and almost flat. Mesospiracle borne at the anterodorsal apex of mesanepisternum. Mesanepisternal suture complete. Mesopleural suture angularly bent; its subhorizontal portion long. Mesomeral fissure present. Mesomeron not intruding into metapleural area.

METATHORAX: Metanotum separated from first abdominal tergite by wide membrane. Posterior intersegmental suture extends almost vertically. Metafurca terminates in two concave, wing-like furcal arms. Each arm branches into an anterior and posterior furcal limb.

Psilocephala sequa (figs. 52; 53a, c; 56c)

CERVIX: Dorsocervicalia elongate and narrow. Laterocervic- alia with subconical, strongly convex bases; their anterior process slightly elongate and narrow. Sella bears two compact bundles of sensilla. It tapers into a long median bar posteriorly.

PROTHORAX: Mid-dorsal collar of antepronotum broad; lateral areas broad and slightly swollen. Postpronotal lobes weakly - 67 - i

swollen; their posterior margins smooth. Proepisternum broadly united to probasisternum. Proepimeron partly separated from mesepisternum by a suture that continues ventrally from the mesospiracular membranous cleft. Probasi- sternum completely divided by probasisternal suture. Basisternal carina weak. Costosternal suture present. Ventral transverse suture present. Sternopleural sutures present. These are rather unusual, they extend posteriorly to reach the anterior margins of the mesocoxal bases without meeting each other along the midventral line.

MESOTHORAX: Prephragma well developed, strongly bilobed. Mesoprescutum strap-like and narrow. Anterior and posterior trans-scutal sutures present. Tergal apodeme reduced. Trans- scutellar suture represented by a shallow impression. Evag- inated part of scutellum of medium size. Subscutellum very weakly distinct. . Mediotergite not delimited by lateral sutures. Laterotergites slightly callose. Mesospiracle embedded in a membranous cleft whose edges are approximated ventrally, until they meet to form a suture that separates the proepimeron and mesepisternum. Mesanepisternal suture lost anteriorly. Mesopleural suture softly bent; subhorizontal portion very short. Mesomeral fissure present, Mesomeron not intruding into metapleural region.

METATHORAX: Metanotum not remarkable. Metafurca terminates in two concave, wing-like furcal arms. Each arm branches into an anterior and posterior limb.

Apiocera trimaculata (figs. 54, 55, 56d)

CERVIX: Dorsocervicalia short and broad. Laterocervic- alia with subconical, strongly convex bases; their anterior processes slightly elongate and narrow. Sella bears two compact bundles of sensilla. It tapers into a long median bar posteriorly. - 68 - i

PROTHORAX: Mid-dorsal collar of antepronotum broad; lateral areas as broad as the collar; slightly swollen. Postpronotal lobes slightly swollen; their posterior margins smooth. Proepisternum separated from probasisternum by membrane. Proepimeron partly separated from mesepisternum by an isolated, weakly distinct suture, sternopleural suture separates it from profurcasternum. Pro- basisternum completely divided by probasisternal suture. Probasisternal carina weak. Costosternal suture present. Ventral transverse suture present.

MESOTHORAX: Prephragma well developed; conspicuously asymmetrical bilaterally. Mesoprescutum strap-like and narrow. Anterior and posterior trans-scutal sutures present. Tergal apodeme reduced. Trans-scutellar suture represented by a deep impression. Evaginated part of scutellum of moderate size. Mediotergite not delimited by lateral sutures. Laterotergites weakly callose. Meso- spiracle embedded in membrane . Mesanepisternal suture lost anteriorly. Mesanepisternal pad present. Mesopleural suture angularly bent; subhorizontal portion long. Meso- meral fissure present. Mesomeron not intruding into metapleural area.

METATHORAX: Metanotum not remarkable. Ventral metapleural arm spatulate, well developed. Metafurca terminates in two concave, wing-shaped lateral arms. Each arm branches into an anterior and posterior limb.

Machimus atricapillus (figs. 57, 58, 63a, 64)

CERVIX: Dorsocervicalia elongate and narrow. Latero- cervicalia with subconical, strongly convex bases; their anterior processes short and broad. The only indication of the sella is the presence of two compact, isolated - 69 - i

sensillar plates borne on the anterior margin of a shiny, membranous area distinctly raised from the surrounding cervical membrane.

PROTHORAX: Mid-dorsal collar of antepronotum broad; lateral areas oval, slightly swollen. Postpronotal lobes elevated and their posterior margins smooth. Proepi- sternum broadly united to probasisternum. Proepimeron indistinguishably fused to mesepisternum but the sternopleural suture separates it from the profurcasternum. 'Basisternum completely divided by basisternal suture. Basisternal carina well developed. Costosternal suture . present .- Ventral transverse suture-present.

MESOTHORAX: Prephragma very narrow basally; terminates into two thick, subparallel prongs. Mesoprescutum subtriangular; tapering posteriorly. Anterior and posterior trans-scutal sutures present. Tergal apodeme well developed - Trans-scutellar suture represented by a deep impression. Evaginated part of scutellum short. Mediotergite not delimited by lateral sutures. Laterotergite differentiated into an upper, weakly swollen and a lower conspicuously swollen area. Mesospiracle embedded in narrow membrane. Mesanepisternal suture lost anteriorly. Mesopleural suture softly bent; its subhorizontal portion very short. Meso- meral fissure present.

METATHORAX: Metanotum not remarkable. Ventral part of posterior intersegmental suture interrupted by a break. Metapleural ridge bears an apodeme near its dorsal limit. Metafurca terminates in two concave, wing-like furcal arms. Each arm branches into an anterior and posterior limb. The latter abuts on the ventral metapleural arm. - 70 - i

Empis livida (figs. 65, 66, 63c, 69a,c)

CERVIX: Dorsocervicalia elongate and taper posteriorly. Laterocervicalia with subquadrangular, flat bases; their anterior processes short and broad. Sella bears two compact bundles of sensilla. It tapers into a narrow, median sclerotised bar posteriorly.

PROTHORAX: Mid-dorsal collar of antepronotum broad; lateral areas broad and almost flat. Postpronotal lobes slightly swollen and their posterior margins smooth. Pro- episternum broadly united to probasisternum. Proepimeron partly separated from mesepisternum by the posteriorly directed ventral portion of the anterior intersegmental suture (vis.j). Probasisternum completely divided by probasisternal suture. Probasisternal carina well developed. Costosternal suture present. Ventral transverse suture absent. Sternopleural sutures absent.

MESOTHORAX: Prephragma well developed and strongly bilobed. Mesoprescutum strap-like and narrow. Anterior trans- scutal suture greatly reduced. Posterior trans-scutal suture present. Tergal apodeme well developed. Trans-scutellar suture represented by a shallow depression. Evaginated part- of scutellum rather short. Subscutellum very weakly convex. Mediotergit£ not delimited by lateral sutures. Laterotergite only weakly swollen. Mesospiracle borne on the anterodorsal apex of the mesanepisternal. sclerite. Mesanepisternal suture lost anteriorly. Mesopleural suture softly bent; its subhorizontal portion very short. Mesomeron intrudes into the metapleural area. The confluent mesofurcal pits are modified into a transverse slit lying behind the mesocoxae. Mesofurca extends as a boat-shaped, open structure terminating in two paired furcal cup s.

METATHORAX: Metanotum not remarkable. As a result of the intrusion caudally of the mesomeron, the posterior intersegmental suture becomes confluent with the metapleural suture, thus dividing the metanepisternum into a dorsal part - 71 - i

(daes^) and a ventral part (vaes^). The metafurca terminates in two concave, wing-like furcal arms. Each arm branches into a long anterior and a short posterior limb. The latter does not attain the weakly developed ventral pleural arm.

Poecilobothrus nobilitatus (figs. 70-72, 74a, 75a)

CERVIX: Dorsocervicalia elongate and narrow. Latero- cervicalia with subconical slightly swollen bases; their anterior processes short and broad. Postcervicale with long, posteriorly directed internal apodeme (pea). A crescentric ventral cervicale (vc) lies transversely between the anterior processes of the laterocervicalia. Sella bears two compact bundles of sensilla. It is almost divided into two parts by a medial constriction.

PROTHORAX: Mid-dorsal collar of antepronotum narrow; lateral areas subquadrangular and almost flat. Postpronotal lobes slightly swollen and their posterior margins smooth. Proepisternum broadly united to probasisternum. Proepi- meron partly separated .from mesepisternum by a posteriorly directed suture (vis^) that arises from the propleural suture. This may be the ventral part of the anterior intersegmental suture. Probasisternum completely divided by probasisternal suture. Probasisternal carina well developed. Costosternal suture obliterated. Ventral transverse suture obliterated. Sternopleural sutures lost posteriorly.

MESOTHORAX: Prephragma well developed; lateral arms broad and are divergent distally. Anterior apex of postpronotal ridge continues into a thin cuticular thread (aphth) that joins the dorsal margin of the prephragma near the median dorsal line. Mesoprescutum strap-like and narrow. Anter- ior trans-scutal suture greatly reduced. Posterior trans- scutal suture absent. Tergal apodeme well developed. - 72 - i

Trans-scutellar suture represented by a deep impression. Evaginated part of scutellum short. Anterior part of mediotergite differentiated into a weakly convex subscutellum. Mediotergite not delimited by lateral sutures. Laterotergite subtriangular and almost flat. Mesospiracle borne on the anterodorsal apex of the mesanepisternal plate. Mesanepisternal suture lost anteriorly. Mesanepisternal pad present; its course is demarcated by a clavate, heavily pigmented area. Mesopleural suture softly bent; its subhorizontal portion very short. Mesanepimeral area lying between the subalar fissure and laterotergite is heavily pigmented.

METATHORAX: Metapostnotum bears an internal apodeme at its ventral limit (pna^). As a result of the intrusion caudally of the mesomeron, the posterior intersegmental suture becomes confluent with the metapleural suture, thus dividing the metanepisternum into a dorsal and ventral part. The metapleural ridge bears a dorsal and ventral apodeme. The former, which arises at the level of the basalar plate, is very weak. The latter arises at the base of the ridge and projects mediodorsally as a well developed clavate arm. The long metafurca branches into two long furcal arms. Each arm terminates in a convex, anteriorly-posteriorly directed head. - 73 -

Table (2) - Character-'Summary

» 1 s- 3 P to P 3 CO O u P CO bO 3 P > o to p P a bC •H CO o c 3 to CO C a <0 CO •rl p 3 S-, p o ca ca B CO G CO (J 3 •H tu u 3 H o P o a CO p B o •H rH o 0) rH o o a a C, u •a o a o o B CO O •H O •H ta CO CJ •H •H rH . o a bC ta >> p o > c rH o P •rl CJ c o p CO o o P a rH rH rH <0( 0 rH > > o P •H X > bO u o O a ca s o <> , CU a. o X X o CCs w EN o cu w cn CU c s w cu o rH CM m •a- LP vO t- CO OV o . rHO J m

PROTHORAX

antepronotum: A - expanded anteriorly. B - not 30

postpronotal lobes: (i) A - large. B - medium-sized. C - much reduced (ii) A - conspicuously swollen. B - slightly so. C - almost flat (iii)A - posterior margins smooth A B B - posterior margins truncate

proepisternum: (i) A - very narrow. B - not so (ii) A - separated from probasisternum by membrane. B - broadly united C A to it. C - narrowly so

proeplmeron; (i) A - partly separated from mesepisternum by suture ABA B - indistinguishably fused to it, (ii) A - divided by an internal ridge into two parts. B - not so

probasisternal suture: A - complete B - lost anteriorly

costosternal suture: A - distinct B - obliterated

ventral transverse suture A - distinct B - obliterated

sternopleural sutures: A - absent B - complete C - lost anteriorly D - lost posteriorly

profurcal pits: A - confluent B - not so

)rospinasternum: A - absent B - present 111I1I - 75 -

o rH CM m in vO c- 00

MESOTHORAX prephragma: (i) A - large. B - medium-sized. A c A E C A C - much reduced (ii) A - strongly bilobed B - weakly so A D A C B A B A C - with one median arm D - margin almost entire mesoprescutum: A - strap-like; narrow B A E A B A B - subtriangular; broad anteriorly. 1 dorsolateral mesoscutal sutures: 1 3 A B A B A B A A - absent. B - present 1 1 anterior trans-scutal suture: 1 1 B C A 3 B C A - absent. B - complete C - reduced l posterior trans-scutal suture: A - distinct. B - obliterated 3 A B A B 1 tergal apodeme: A - large. B - medium-sized A B A B A C A C - greatly reduced trans-scutellar suture: A - represented by deep impression A E A B A B A B - shallow depression evaginated part of scutellum: A - large. B - medium-sized A B A B C B C - greatly reduced scutellar spines: A - absent or number, if present A 4 A 2 \ subscutellum: A - not differentiated. B - strongly A B C A C A convex. C - weakly so mediotergite: (i) A - large. B - medium-sized C B C B A B / B C - greatly reduced (ii) A - delimited by lateral sutures. A B A B B - not so 1 1 1 1 1 1 1 1 1 - 76 -

o rH C\J m -T in v£> t— oo CTN o rH CM CO rH rH rH rH rH rH rH rH rH rH CM

MES0TH0RAX

30 postphragma: A - ridged B B B - not ao 1 1 1 1 1 1 1 31 laterotergite: (i) A - large. B - medium-sized A B A C A c B A B C - greatly reduced (ii)A - conspicuously callose B - slightly so A C B C A C A B A C B A C C - almost flat 1 1 32 mesospiracular membrane: A - wide

B - greatly reduced A C B A B C A B A C C - secondarily sclerotised 33 mesanepisternal suture: | 1 A - complete | A B A B A B A B B - lost anteriorly 1 1 1| 34 mesanepisternal pad: I A - absent A B B A B B - present I I 1 I 1 1 I 1 1 35 mesopleural suture: A 0 B A (i) A - angularly bent. B - not so (ii)A - horizontal portion long. B A B ? C A B A B B - short. C - indiscernible I 1 I 1 36 mesomeral fissure: 1 A - absent B - large A C A C A B C A E A C - reduced | 1 | | 1 1 1 | | 37 mesomeron: A - not intruding into metapleuron B - strongly intruding C A B

C - weakly so 1 | 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 —r 1 I 38 posterior intersegmental suture: A - confluent with metapleural suture R A B - not so

1 I 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 - 77 -

o rH OJ cn< r in c- co a>o rH OJ cn

METATHORAX

39 metanotum: (i) A - overlapped by first A B A B B A B A abdominal tergite. B - not so (ii)A - metanotal apodeme distinct B B - not so

40 dorsal metapleural apodeme: A - distinct. B A B - not so 1 1 1 1 "1 1 1 1 1 41 metepisternum: 1 1 1 1 1 1 1 1 1 1 1 1

(i) A - expanded anteriorly B A B B - not so (ii)A - divided into a dorsal and neutral part due to intrusion of mesomeron B A B - not so 1 1 1 1 1 1 1 1 1 1 1 1 1 42 metepimeron: 1 1 II 1 1 1 1

(i) A - indistinguishably fused to B A B first abdominal tergite. B - not so

(ii)A - meets its counterpart behind B A B metacoxae. B - not so

43 ventral metapleural arm: 1 1 1 1 1 1 1 1 1 (i) A - well developed. B - not so B A 3 A E A (ii)A - rod-shaped. B - spatulate ] D C B D C B A C - hump-like. D - almost'flat 1 1 1 1 1 1 1 I 1 1 44 metafurca: A - terminates in two lateral arms A B A B - in a single median structure 1 1 Mill 1 1 1 1 1 1 1 lateral view of the thorax of Atylotus agrestis with details of sutures psc2 npla2 p|wp2 anwp2 I .Omm

lateral view of the thorax of A. agrestis with details of sclerites 1.0 mm ppsca2

lscr2 tga2

00 O

aemr2

UJ 2 cxb3 lateral internal view of the thorax agrestis with details of endoskeleton 1.5mm I.Omm

sternum of A. agrestis. a-ventral view; b-dorsal internal view - 82 - i

5 Haematopota patellicornis

Chrysops brucei

ventral view of the probasisternum in Tabanidae I - 83 - 6 0.5mm

posterior internal view of the prephragma of Aj agrestis -

posterior internal view of the metafurca of A_. agrestis - - 84 - i

lateral view of the thorax of Pelecorhync hus fuscon iger - 85 - i 8

lateral view of the thorax of Pantophthalmus tabaninus - 86 - i 9

ventral view of the probasisternum of Pelecorhynchus fusconiger.

1.5mm

ventral view of the probasisternum of Pantophthalmus

tabaninus - - 87 - i

Pelecorhynchus fusconiger

Pantophthalmus tabaninus

posterior internal view of the prephragma - 88 - II

0.5mm

;elp2

sscl,

It-

aes3 em

pes2

lateral view of the thorax of Chorisops tibialis - 89 - i

0.5 mm

lateral internal view of the thorax of C. tibialis 3 0*5 mm

sternum of C. tibialis. a-ventral view; b-dorsal internal view. \ - 91 - i

14 Berjs chalybeata 0.33 mm

Merosargus st a mineus 0.5

ventral view of the probasisternum in Stratiomyidae - 92 - i

1.0 mm Stratiomys chamaeleon

Hermetia illucens 0-75

b J

ventral view of the probasisternum in Stratiomyidae - 93 - i

Chorisops tibialis

0.17 mm

Pachygaster atra

posterior internal view of the prephragma in Stratiomyidae _ 9 4 _

Hermetia illucens

Merosargus stamineus

0.33

posterior internal view of the prephragma in Stratiomyidae - 95 - i

2.0 mm

lateral view of the thorax of Xylomya tenthredinoides

1.0 b —

lateral view of the thorax of Xylophagus fulgidus - 96 - i

0.5 mm Xylophagus fu Igidus

Xylomya tenth red inoides 0.75 b

ventral view of the probasisternum - 97 - i

20 0.33 mm

Xylophagus fulgidus

Xylomya tenthredinoides 0.5

posterior internal view of the prephragma - 98 - i

^ \ lateral view of the thorax of Coenomyia ferruginea a-external; b-internal • - 99 - i

22 0.5 mm a

posterior internal view of the prephragma of Cj ferruginea

0.75 b

ventral view of the probasisternum of

C . ferruginea - 100 - i

1.0mm

lateral view of the thorax of Rhagio scolopaceus - 101 - i

I • 0 mm

lateral internal view of the thorax of scolopaceus - 102 - i

0-5 mm 25

lateral view of the thorax of Hilarimorpha sidora

lateral view of the thorax of Vermileo sp. - 103 - i

scolopaceus Atherix ibis

Chrysopilus cristatus Verrnileo sp.

probasisternal variation in Rhagionidae - 104 - i

FL scolopaceus Atherix ibis

0 • 5 m m

Chrysopilus cristatus Vermileo sp

0.5 0.13

prephragmal variation in Rhagionidae - 105 -

28 0.13 mm

posterior internal view of the prephragma of

H . sidora

ventral view of the probasisternum of H. sidora K> lateral view of the thorax of Exhyalanthrax lugens l-Omm

pph O

aesr2 Ul lateral internal view of the thorax lugens 2.0mm sg2 b abc- abti abs

i—j o oo

es1 em 1.5mm pis.

UJ thorax of Systropus edwardsi . a-lateral view,- b-posterior view of the metathorax E E o m CO

ventral view of the cervix and probasisternum. a-Exhyalanthrax lugens. w to

b- Bombylius major i M 1—' 0 1

ventral view of the cervix and probasisternum - a-Enica longirostris u> UJ b-Callostoma fascipennis. - Ill -

Heterotropus indicus

0-25 mm

Systropus edwardsi

probasisternal variation in Bombyliidae - 112 -

Bombylius major B. discoideus

0.5 mm

CallostoMa fascipennis Usia aenea

prephragMal variation in BoMbyliidae - 113 -

Exhyalanthrax lugens Exprosopa minos

0.17 mm abcf

Villa sexfasciata Heteralonia megerle

Tomomyza pictipennis Anthrax pithecius

0.33 prephragmal variation in Bombyliidae - 114 -

Systropus edwardsi

Exhyalanthrax lugens - 115 -

Bombylius discoideus B . major

Exprosopa aurulans E_. louisae - 116 -

39 Usia aenea Toxopho ra maculata b

0.5 mm 0.75

Phthiria gaedii Tomomyza pictipennis

metafurcal variation in Bombyliidae - 117 -

I.Omm

sc2

anr mt-

\ aes2 \ •4th. ax 2 \ es. \ lt2 pes2 bsf em em

lateral view of the thorax of Ogcodes gibbosus - 118 -

ventral view of the thorax of O • gi bbosus - 119 -

Eulonchus tristis

Acrocera globulus

probasisternal variation in Acroceridae - 120 - i »

O • gibbosus A . globulus

0 • 5 mm

prephragmal variation in Acroceridae

•vpla3

0-75

posterior internal view of the metafurca

of O. gibbosus - 121 -

tgtb2

1.5 mm

lateral view of the thorax of Prosoeca accincta - 122 -

0*75 mm

posterior internal view of the prephragma

of P. accincta - 123 -

46 Fallenia fasciata Neorhynchocephalus sulphureus

probasisternal variation in Nemestrinidae

1.0

posterior view of the postphragma of p. accincta - 124 -

1.5mm

lateral view of the thorax of Ectyphus pinguis - 125 -

48 3*0 mm

lateral view of the metathorax of Mydas clavatus - 126 -

49 Ectyphus pinguis Mydas clavatus

0 • 5 0.75

prephragmal variation in Mydidae

0.5

ventral view of the probasisternum of E . pinguis - 127 -

Q»75 mm

lateral view of the thorax of Scenopinus fenestra!is a - external; b - internal » - 128 -

0-25 mm

posterior internal view of the prephragma of S. fenestralis

0-33

ventral view of the probasisternum of S. fenestralis - 129 -

V /

1.0 mm

lateral view of the thorax of Psilocephala sequa - 130 -

P. seq ua Lindneria sp. b

0.5mm

prephragmal variation in Therevidae

fs,

splsf 0-75

Ims

ventral view of the profurcasternum of P. sequa - 131 -

/ / / / a / / V

1.5 mm

lateral view of the thorax of Apiocera trimaculata - 132 -

0 . 5 mm

posterior internal view of the prephragma of A . trimaculata

ventral view of the probasisternum of A_. trimaculata \ - 133 -

54 Prosoeca accincta Ectyphus pinguis

1,0mm

Psilocephala sequa Apiocera trimaculata

IT)

ventral metapleural arm in Brachycera - 134 -

pes2 aes3

1.5 mm

lateral view of the thorax of Machimus atricapillus a - external; b - internal. 1.0 mm a b

1/1 00 sternum of hi. atricapillus a-ventral view; b dorsal internal view 0.75mm

ui thorax of Leptogaster cylindrica. a-lateral view; b-posterior view of the metathorax SO - 137 -

Ommatius parvulus Willistonia nigrofemorata

0 • 5 mm

0.75 0,5 probasisternal variation in Asilidae - 138 -

61 Zabrops t_. tagax Atoniomyia duncani

0 -75 mm 0-5

Trie lis sp Laphria columbica d V ~

1.5

Leptogaster cylindrica Haplopogon erinus - 139 -

Efferia albibarbis Ommatius parvulus

0-5 mm

Laphria columbica Ospirocerus abdominalis

o 1.5

Zabrops t. tagax Willistonia nigrofemorata

0.5 prephragmal variation in Asilidae - 140 -

Machimus atricapillus Hodophylax tolandi

0«5mm

Haplopogon erinus Atomosjella antennata

0.5

Blepharepium vorax Leptogaster hesperis e,

prephragmal variation in Asilidae - 141 -

I .Omm 54

a-lateral view of the pterothoracic furcae of M. atricapillus

vcxp3

b-posterior internal view of the metathorax of M. atricapillus - 142 -

lateral view of the thorax of Empis livida • a-external ; b-internal. - 143 -

0.5 mm

dorsal internal view of the thorax of E. livida - 144 -

Chelifera praecatoria 67 0-75 mm

daes

Drapetis laevis

lateral view of the thorax in some Empididae - 145 -

68 Clinocera stagnalis Phy llodromia melanocephala

bs1 b

fpt

0.5mm

Empis livida Trichopeza longicornis

probasisternal variation in Empididae - 146 -

69 Empis livida Clinocera stagnalis

0 • 5 mm

prephragmal variation in Empididae

E . livida Cj stagnalis

0-5

Platypalpus pallidiventris Ocydromyia glabricula f

metafurcal variation in Empididae - 147 -

0-75 mm

sscl2

Pni

vis. an mm vc-

esj des-

bsf em3

iss2 ves3+pes3

lateral view of the thorax of Poecilobothrus nobilitatus - 148 -

0-75 mm

aesp2

pph

pea-

pis/

lateral internal view of the thorax of P. nobilitatus view ; dorsal internal view . ^ - 150

73 Australiola zonatus Argyra diaphana b

0-5rn m

Machaerium maritimae Campsocnemis curvip

Liancalus virens Medetera trunco rum

probasisternum in some Dolichopodidae - 151 -

Poecilobothrus nobilitatus Liancalus virens apth

Argyra diaphana Australiola zonatus

0 • 5 mrn

Aphrosylus celtiber Medetera truncorum

prephragmal variation in Dolichopodidae - 152 -

pterothoracic furcae in some Dolichopodidae

P. nobilitatus Liancalus virens

metapleuron in some Dolichopodidae - 153 -

Aphrosylus celtiber Liancalus virens a

0*5 m rn

Australiola zonatus Medetera truncorum

metafurcal variation in Dolichopodidae - 154 -

V SYSTEMATIC SURVEY

Two suborders are usually recognised in the Diptera, the Nematocera and Brachycera. The latter is further subdivided into the Orthorrhapha and Cyclorrhapha. In the present discussion, the term Brachycera is applied in a restricted sense to stand for the Orthorrhapha, a usage already sanctioned by Oldroyd (1969) and Imms (1977). Hennig (1954 and later) has introduced a more elaborate system in which he progressively divides the order into sister groups of infraordinal ranks. By this scheme the Brachycera sensu stricto falls into two infraorders, the Tabanomorpha and Asilomorpha. These groups correspond to the orthodox super- families Tabanoidea and Asiloidea, respectively. Brauer (1883) has set apart as the HOMOEODACTYLA all the families of Brachycera in which the pretarsus is furnished with three similar pads, i.e. the empodium is pulvilliform. Hennig (1969) presumably accepting Brauer's views, designates the rest of the suborder, in which the empodium is either absent or replaced by a bristly hair, as the HETERODACTYLA. How- ever, Hennig takes the paradoxical decision of including the Acroceridae in the HOMOEODACTYLA, while he assigns the Nem- estrinidae to the HETERODACTYLA. In both familes the pretarsus has three subequal pads. Oldroyd (1969) believes that the two families are closely related to the Bombyliidae; he regards the persistent pulvilliform empodium as an example of the retention of primitive characters. The empodium is either greatly reduced or completely lacking in the Rhagionid Vermileoninae (Teskey, 1981), while the Empidid Clinocerinae possess a well developed pad-like empodium (Collin, 1961). The fate of the pulvilliform empodium has not been satisfactorily clarified. The evolution of this organ (excluding its complete loss) might have followed one of the following paths:-

1. The broad empodium has been modified into a bristle- like structure. In this case, the two forms would be considered as two phases of expression of the same feature, i.e. they are homologous structures. \ - 155 -

2. The fleshy empodium has been completely lost and was replaced by a newly acquired bristly hair. This possibility is implied in the carefully worded statement by Brues _et al» (1954) that "empodium wanting or replaced by a bristly hair". This suggests that the two organs have different origins, i.e. they are analogous. Either way the pulvilliform empodium seems to represent the more ancestral condition. As thus it cannot be used as a constitutive character. Hence the concepts of HOMOEODACTYLA and HETERODACTYLA have no place in the systematics of Diptera.

The means at present available for dividing the Brachy- cera into subgroups are not satisfactory; the chief features so far used in establishing relationships, such-.as the annulation of the antennal flagellum, the wing venation and the nature of the empodium, suggest different conclusions.

In the survey that follows, I divide the Brachycera directly into families. The families here considered are the Tabanidae, Stratiomyidae, Rhagionidae, Bombyliidae, Acroceridae, Nemestrinidae, Mydidae, Asilidae, Empididae and Dolichopodidae.

TABANIDAE (Figs. 1-6)

The Tabanids form a large and compact group of conspicuous flies. Because of their economic importance as pests of livestock, they have attracted much attention from students of Diptera. Despite this, they are inadequately known taxonomically because of an embarrassing deficiency of diagnostic characters.

In subdividing the family considerable importance has been ascribed to the tibial chaetotaxy, basicostal hairiness and the annulation of antennal flagellum. The equivalents of these characters are insufficient even to discriminate - 156 - species in highly diverse families like the Asilidae and Dolichopodidae.

Recent treatises divide the family into the Tabaninae, Pangoninae (including Scepsidini) and Chrysopsinae. From a study of the condition of the probasisternum, I found that this organ is fused to the proepisternum in Chrysops, Nemorius, Silvius and Adersia but separated by sunken membrane in Tabanus, Haematopota, Ancala, Atylotus and Philoliche. I regard the united probasisternum as a constitutive character and tentatively include all species showing this phase in one subfamily, which is the Chrysop- sinae. If all the Scepsidini conform to the condition found in Adersia, they should belong here.

There is no thoracic feature that can be used to separate the Tabaninae from the Pangoninae, but the head characters, which are traditionally employed for this purpose, seem quite sufficient.

The prephragmata and metafurcal arms do not show any structural variation that can help in characterising genera. The only feature that may be of limited use on this level is the shape of profurcasternum, especially the portion embraced between the arms of the V-shaped costosternal suture.

STRATIOMYIDAE (Figs. 11-17)

This is a highly diverse family whose thoracic morphology does not incorporate derivative features that can unite it into a discrete group. However, some of its genera possess a combination of peculiar characteristics that do not occur in the same combination elsewhere in the Brachy cera. Among these are:-

1. In some genera the scutellum is armed with marginal spines which may be two in number and well developed, as - 157 - in Stratiomys, or more than a dozen and papilla-like, as in Beris. Coenomyia is the only non-Stratiomyid genus that possesses scutellar spines.

2. The mesanepisternum of some genera, such as Chorisops, is traversed by an oblique internal ridge that I called the "anepisternal pad", a term first introduced by Ulrich (1971) to designate an analogous structure in the Dolichopodidae. The presence of a similar structure has also been noted in Psilocephala and Apiocera.

3. Many genera possess on the posterodorsal margin of the haltere base a finger-like hairy structure. This organ is very conspicuous in Hermetia and Merosargus but apparently absent from Chcrisops.

4. In a few genera, the probasisternum is greatly expanded anteriorly. This is particularly noticeable in Beris, in which the medially grooved expanded area completely overlaps the postcervicalia.

5. The probasisternal suture may be much reduced as in Hermetia and Stratiomys.

6. The anterior part of the postnotum is differentiated into a strongly convex subscutellum. Ulrich (1971) thought this character is peculiar to the Empidoidea. .Curran (1924,) has reported its occurrence in the Tachinidae, Syrphidae and Stratiomyidae. This character seems to be more widely distributed in the Diptera than was previously thought. Its evolutionary history is unknown and it does not seem to be a reliable taxonomic character.

Taking into account the size of the family, it seems unwise to make generalisations from the observations made on a limited number of species but I do believe that the integration of the above characters in the systematics of Stratiomyidae is likely to result in an improved classification of this family. - 158 - ?

From an examination of the shape of the prephragma, I found that it shows only slight variation within the Stratiomyinae (Stratiomys, Qdontomyia), Beridinae (Beris, Chorisops) and Sarginae (Merosargus, Microchrysa, Sargus) but considerably variable within the Clitelleriinae (Oxycera, Vanoyia)

RHAGIONIDAE (Figs. 23-27)

Historically the concept of Rhagionidae has been used loosely to include a miscellany of heterogeneous genera, most of which now stand as separate families on their own, such as Hilarimorpha, Xylomya ^ Xylophagus and Coenomyia (Leonard, 1930). More recent departures are Atherix and Vermileo. Even after all this pruning, the genera remaining in the family have no thoracic feature that unites them as a distinct group. If the basis on which the Athericidae is given full family rank is valid, the Rhagionidae may eventually end up with very little more than Rhagio.

Structurally Atherix is not more different from Rhagio than is Chrysopilus. On the other hand, Vermileo differs considerably from the other Rhagionids seen. Its position is analogous to that of Leptogaster among the Asilidae and Systropus in the Bombyliidae.

As far as the species examined are concerned, the pre phragma seems to provide a good generic character. The sella, probasisternum and metafurca can also be used as supplementary characters on the genus level. A better understanding of generic delimitation seems to be a pre- requisite for a more precise definition of the family. - 159 -

Table (3): Subfamilies of Bombyliidae

Bezzi (1924) Brues et al Hull (1973) Bowden (1980) (1954)

1. Bombyliinae Bombyliinae Bombyliinae Bombyliinae 2. (D+ Conophorinae (1) (1) 3. Mariobezziinae Mariobezziinae (1) (15) 4. Heterotro- Heterotro- (1) Heterotro- pinae pinae pinae 5. Cyrtosiinae Cyrtosiinae Platypyginae (6) 6. (5) Mythicomiinae Mythicomiinae Mythicomiinae 7. Phthiriinae Phthiriinae Phthiriinae Phthiriinae 8. (7) (7) Gerontinae (11) 9. Usiinae Usiinae Usiinae Usiinae 10. Systropinae Systropodinae Systropodinae (11) 11. Toxophorinae Toxophorinae Toxophorinae Toxophorinae 12. Cylleniinae Cylleniinae Cylleniinae Cylleniinae 13. (0) (0) Xenopro- Xenopro- sopj.nae sopinae 14. (1) (*) (1) Oniromyiinae 15. Cythereinae Cythereinae (1) Cythereinae 16. (12) Tomomyzinae (12) Tomomyzinae 17. Lomatiinae Lomatiinae Lomatiinae Lomatiinae 18. (17) Aphoebantinae (21) 19. (17) (16) (17) Antoniinae 20. Exopro- Exopro- Exopro- (21) sopinae sopinae sopinae 21. Anthracinae Anthracinae Anthracinae Anthracinae

+ number between brackets indicates the subfamily to which that group belongs under a particular system

0 group not erected

* group not included - 160 -

BOMBYLIIDAE (Figs. 29-39)

This is a large and very diverse group and its systematics are far from settled. According to the present study, the only thoracic character that unites the family is the presence of a well differentiated, narrow, wedge- shaped sclerite (tgflg) that extends obliquely between the lateral scutal suture and the tergal fissure and bears the tergal apodeme internally. I designate this structure the "tergal fulcrum".

For many years, the family was considered to comprise two major groups, i.e. the Bombyliinae and Anthracinae. Further subdivision was made by several authors, Becker (1913) recognised 15 subfamilies and Brues et al (1954) no fewer than 17. Bezzi (1924), using the shape of the eye as a basis for his classification, has divided the Bombyliidae into the series H0M0E0PHTHALMAE in which the hind margin of the eye is entire and the series T0M0PHTHALMAE in which the Hind margin of the eye is indented. This author included ten subfamilies in the former series and three in the latter. Table (3) gives a summary of the schematic divisions as suggested by Bezzi (1924) and seme later authorities.

In the present investigation, the form of the sella has been examined in 15 species representing 15 subfamilies (according to the arrangement adopted in the British Museum (N-H)). It has been found that there are two major types of sella: a type A sella similar to that of Exhyalanthrax and a type B sella exemplified by that of Bombylius. In Exhyalanthrax the sella is greatly attenuated anteriorly, thus forming a spear-shaped structure (Fig. 32,a) while in Bombylius the anterior margin of the sella is roughly rounded (Fig. 32,b). In Callostoma and Enica (Fig. 33,a,b) the sella is weakly attenuated anteriorly but it is not spear-shaped.

Species with type A sella are:- - 161 -

1. Anthrax pithecius (Anthracinae) 2. Exhyalanthrax lugens (Exoprosopinae) 3. Lomatia sabea (Lomatiinae) 4. Tomomyza pictipennis (Tomomyzinae)

Species with an intermediate form are:-

5. Callostoma fascipennis (Cythereinae) 6. Enica longirostris (Cylleniinae)

Species with type B sella are:-

7. Bombylius major (Bombyliinae) 8. Cephalodromia fusca (Cephalodromiinae 9. Conophorus fuliginosus (Conophorinae) 10. Heterotropus indicus (Heterotropinae) 11. Mythicomyia pusillima (Mythicomyiinae) 12. Phthiria gaedii (Phthiriinae) 13. Systropus edwardsi (Systropodinae) 14. Toxophora maculata (Toxophorinae) 15. Usia aenea (Usiinae)

I suggest that, by using the form of the sella as a major criterion of affinity, the Bombyliidae, except the Cylleniinae and Cythereinae, is divisible into two large subordinate groups which may be regarded in a broad sense as series or subfamilies, namely the Anthracinae and Bom- byliinae. The arrangement agrees broadly with Bezzi's concept of the' T0M0PHTHALMAE and HOMOEOPHTHALMAE. The Anthracinae corresponds to the former series and the Bomby- liinae to the latter. Bowden (1980) has expressed a sound, though radical, view when he suggested the Bombyliidae can be divided into two major families, namely the Bombyliidae and Anthracidae, without precluding the possibility of treat ing the Toxophorinae (including Systropodinae) as a distinct family.

The condition of the cervicalia is closely.associated with the state of the sella as shown below:- - 162 -

1. In Exhyalanthrax the dorsocervicalia are elongate and strap-like, while in Bombylius they are short and broad.

2. In Exhyalanthrax the base of laterocervicale is subquadrate, almost flat and its anterior process greatly prolonged and narrow, whereas in Bombylius the base of this sclerite is subconical, strongly convex and its anterior process is short and broad. In both Callostoma and Enica the laterocervicale approaches the condition found in Exhy- alanthrax .

3. In Exhyalanthrax the postcervicalia extend longitudinally and not transversely as in Bombylius. Callostoma and Enica have an intermediate form.

4. In Exhyalanthrax the ventral cervical area is occupied by a thick, shiny membranous flap connected with the sella by a cuticular thread. In Bombylius this area is uniformly membranous without any differentiated structures in it. In Enica the ventral cervical area is similar to that in Bomby- lius , while in Callostoma both the membranous flap and cuticular thread connecting it to the sella are well developed.

5. In Exhyalanthrax the corniculae are displaced inwards and forwards, so forming a sheath that surrounds the protracted sella, while in Bombylius the corniculae extend transversely in front of the sella. In both Callostoma and Enica the corniculae extend transversely.

Other characters which have been considered are the prephragma, probasisternum and metafurca. The prephragma is generally greatly developed and strongly bilobed in Bomby- liinae sensu lato, but rudimentary and only weakly bilobed or its distal margin may even be entire in the Anthracinae. In Callostoma the prephragma is well developed and bilobed (Fig. 35c), but in Enica this organ is vestigial and only weakly indented distally.

The probasisternum shows a considerable degree of \ - 163 - I

variation within the Bombyliinae, being very narrow in Heterotropus and very broad in Systropus. In all the Bomby- liinae seen the probasisternum is separated from the proepisternum by membrane. On the other hand, the probasisternum demonstrates very slight variation within the Anthracinae. In Anthrax, Spogostylum, Tomomyza and Antonia, a strongly sclerotised area connects it to the proepisternum but in Exoprosopa and allies the boundaries of both probasisternum and proepisternum fade into an area that can possibly be described as pigmented membrane. In Callostoma and Enica the probasisternum is broadly triangular, tapering posteriorly (Fig. 33), approaching that of Systropus.

It is clear from the foregoing discussion that Cylleniinae and Cythereinae are connectant groups, the former being nearer to the Bombyliinae, while the latter shows greater affinity to the Anthracinae, but neither could be assigned to its representative group except on negative evidence. These two "subfamilies" have never been satisfactorily placed in the system. Bezzi (1924) has assigned both by their simple eyes to the HOMOEOPHTHALMAE and was followed by Austen (1937). Hull (1973) has included the Cylleniinae in the TOMOPHTHALMAE while he combined the Cythereinae with the Bombyliinae sensu stricto.

Many distinctive thoracic features separate Toxophora and Systropus from the rest of the Bombyliidae examined and this is especially true of Systropus.

Toxophora is distinctive in that it has a very broad antepronotal transverse collar, and its pleural and sternal sclerites have shifted forwards so strongly that this fly seems to be sitting on its tail. A character which Toxophora shares with Systropus is the modification of the sides of the mesonotum into wing-like flaps, which partly conceal the wing bases and basalar sclerites.

The following features distinguish Systropus from all other Bombyliidae studied:- - 164 -

1. The prothoracic furcal pits are confluent; this character is not reported in any other Diptera.

2. The genus possesses a distinct spinasternum and the median spinal pit invaginates to form a well developed forked spina whose arms unite with the corresponding profurcal arms in front of them.

3. Each side of the scutellum bears a membranous flap (sg£) between the posterior notal wing process and axillary cord. Williston (1901) called it the strigula, Verrall (1909) the membranous tubercle. This organ could be a modified calypter, a structure thought otherwise to be absent in Systropus (Brues £t al, 1954).

4. The mesopleural suture extends almost vertically from the coxopleural articulation to the wing base, recalling the Nematocera.

5. The greatly enlarged metepisternum has expanded anteriorly, with a resulting crowding of the mesomeron into a very narrow area above the mesothoracic coxa.

6. The metepimeral plates are extensively sclerotised and they expand ventrally to meet each other behind the metathoracic coxae, thus forming a cone between the hind coxae and abdomen. The line of fusion of the two sclerites is obliterated on the anterior ventral part of the cone though a narrow membrane separates them more posteriorly.

7. The metafurca is modified into a median cup-shaped structure tapering posteriorly. In all other Bombyliidae seen, the metafurca terminates in two lateral arms.

Handlirsch (1908) has put forward the view that Systropus and Toxophora represent two very old evolutionary branches, the former of which belongs near to the base of the Bombyliinae branch, while the latter lies near the bottom of the Anthracinae branch. Bezzi (1924) placed - 165 -

both genera in the series HOMOEOPHTHALMAE. Judging by the unusual characters exhibited by Systropus, it seems plausible to postulate that this genus, and perhaps Toxo- phora , as well, has departed from the main trunk long before the rest of the stock had differentiated into the two major series. Otherwise it would be difficult to explain the presence in Systropus of a very peculiar feature like the spinasternum. According to Ferris (1940b), the confluent furcal pits represent the primitive condition. Weber • (1928) and Snodgrass (1935) argued that, primitively, the furcal pits are widely separated and that when they are set close together this is a secondary condition resulting from the invagination of the sternal plate lying between the pits. With the present state of knowledge, it is difficult to substantiate either view. However, it is remarkable to note that the anterior part of the profurcasternum is not invaginated. medially in Systropus. The other characteristics enumerated are inadequately known in other Diptera, so that it is difficult if not impossible to say whether these are ancestral or derived.

Several thoracic characters show a considerable degree of variation below the level of the subfamily sensu stricto and could perhaps be employed for the purpose of generic differentiation. Among these are the form of the prephragma, the shape of the metafurca and, though of less significance, the condition of the mesanepisternal suture.

An examination of the prephragma has indicated that some of the larger genera, e.g. Bombylius (Fig.35' a,b), may be aggregates of two or more distinct genera. The shapes of the metafurca (Fig. 38 a,b) give supporting evidence for this view. Professor J.Bowden (pens. comm.) has reached identical conclusions from a study of female genitalia in Bombyliidae. - 166 -

ACROCERIDAE (Figs. 40-43)

This is a small family of about 500 species and 50 genera. It exhibits a degree of diversity in form seldom seen in a family of this size. Because of the pullvilli- form empodium, the family is often keyed out with the Tabanoidea, but the reduced antennal segmentation, as well as many other characteristics, qualifies it for a place among the more derived Brachycera.

Brues ej: al_ (1954) use the form of the antennal flagellum to divide the family into two major groups, the Panopinae, in which the flagellum is large and lacks a terminal style, and the Acrocerinae/Philpqtinae complex, in which the flagellum is small and bears a terminal style. They distinguish the Acrocerinae from the Philpotinae by the fact that the postpronotal lobes are widely separated in the former, while they fuse to form a continuous shield in front of the mesonotum in the latter.

The family is united into what is probably a monophyletic group by several characteristics which are unevenly distributed among its members but not found in that combination elsewhere within the Brachycera. All known Acrocerid larvae are parasitic on spiders and this fact, perhaps more than morphological evidence, provides a firm basis for establishing the family as a natural unit.

The degree of morphological variability evident below the subfamily level is striking. In Qgcodes the antennae are placed directly above the margin of the buccal cavity. Psilodera they are shifted to the upper third of the head. In Acrocera they are crowded against the ocelli at the top of the head. In Eulonchus they occupy an island in the middle of the frons, while the eyes touch both above and below them. The proboscis is very long in both Eulonchus and Psilodera, but vestigial in Acrocera and completely lacking in Ogcodes. In this genus the probasisternum is narrowly united to the strap-like, narrow proepisternum but separated - 167 -

by membrane in the other genera. Acrocera has a weakly bilobed prephragma in which the lateral arms are widely separated. In the other genera this organ tapers into a single median arm.

These features, together with several others not mentioned here, when combined with the pattern of geographical distribution, make the study of this family a very easy task. An insuperable difficulty is, however, the paucity of the insects!

NEMESTRINIDAE (Figs. 44-46)

Some authors put the Nemestrinidae and Acroceridae in the HOMOEODACTYLA because they possess a pulvilliform empodium. In several other characters, the two families are very derived and closely related to the Bombyliidae (Oldroyd, 1969). A character shared by the two families is the reduction of the proepisternum to a narrow, strap-like sclerite. In some Nemestrinidae and all Acroceridae, the antennal style is fused to the basal flagellar segment, a character not shown by any other Brachycera (Hennig, 1969; Bernardi, 1973).

One derived character that unites the Nemestrinidae into a monophyletic group is the presence on the outer surface of the postphragma of two ridges, one on each side, that extend longitudinally from the proximal to the distal margin of this organ.

Bernardi (1973), basing his classification on the form of the female ovipositor, has divided the family into two major groups. The first group, which consists of the Hirmoneurinae, Nemestrininae and Cyclopsidiinae, is char- acterised by the possession of a telescope-shaped ovipositor. The second group, containing the Trichopsideinae and Atria- dopsinae, possess a sabre-shaped ovipostor. I - 168 -

On the genus level Bernardi (op. cit.) uses the state of the antennal style, whether it is separated from the basal flagellar segment or fused to it, and the form of the proboscis, whether longer or shorter than the head. The same author recognises only 15 genera, one of which, namely Trichopsidea, contains three species, one in the Americas, one Euro-African (extending from the Caucasus to the Cape) and one in Australia. He comments that the separation of the species is based solely on their geographical distribution.

The species seen here, i.e. Fallenia fasciata, Neorhynchocephalus sulphureus and Prosoeca accincta, possess dissociated probasisterna of characteristic shapes. This suggests that the potential value of the probasisternum as a diagnostic character deserves consideration.

In Prosoeca there is, on each side of the scutum, a small but distinct tubercle (tgtbg) that arises at the base of the posterior trans-scutal suture. Among the 38 characters examined by Bernardi (1973) the only thoracic skeletal structure considered is the postnotum.. It seems likely that a closer investigation of the thoracic morphology may yield some useful characters that were so far overlooked.

MYDIDAE (Figs. 47-49)

The Mydids form an unusual group of flies that are regarded as relicts of the past (Oldroyd, 1964). The family is unquestionably monophyletic and there is hardly any need to search for characters to establish this; rather the problem is to find features that would suggest a particular relationship to any of the other Brachyceran families.

One conspicuous feature of the group is the great reduction of the prothorax, which gives these flies the - 169 -

appearance of a narrow-necked bottle. This is further emphasised by the subclyindrical shape of the body.

Taking into consideration the bulky size of most Mydids, some structures such as the mesofurcal cups and basalar apodeme seem disproportionally reduced. The evaginated part of the scutellum is represented by a narrow, transverse belt that leaves the whole of the postnotum exposed. The tergal fissure is greatly reduced and the tergal apodeme is indiscernible. As this apodeme provides point of insertion for the posterior tergal muscle of the mesobasalare, it is very unlikely to be completely lost; a careful tracing of this muscle from its origin to its point of insertion near the tergal fissure may help to locate' a vestige of the apodeme.

The prothoracic transnotal ridges continue dorsally to meet each other along the median dorsal line, thus forming a broad arch from which the prephragma descends. In all other Brachycera studied, the transnotal ridges terminate at the lateral edges of the prephragma.

The members of this family represent a highly per- fected and fascinating piece of body architecture. The metathorax seems to be modified in order to play a greater role in flight mechanism than is the case in other Brachycera. The hind limbs are stoutly built and much more Orthopteroid than Dipteroid. The metanepisternum is enlarged at the expense of the mesomeron and occupies practically the whole ventral area between the middle and hind limbs. Posteriorly, the metepimeron is indistinguishably fused to the first abdominal tergite. In Mydas the metepimeron bears a large tubercle that Young (1921) considered to belong to the first abdominal tergite. The nature of this tubercle has already been discussed (cf p.37).The metafurca is well developed and the posterior metafurcal limb fused to the ventral metapleural arm. These structural modifications would be better understood if the musculature had also been studied. However, - 170 -

it seems plausible to suggest that strengthening of the metathorax would give the robust flies extra leverage at the take-off.

ASILIDAE (Figs. 57-64)

The form of the sella is sufficiently distinct both to unite the family as a discrete group and to distinguish it from other Brachycera. This organ consists of two isolated, compact sensillar plates borne on a raised, shiny membranous area, a form not known elsewhere among the Brachycera.

Hardy (1948) introduced in the classification of the Asilidae the nature of the probasisternum, i.e. whether it is separated from the proepisternum by membrane or fused to it. Clements (1951) who examined the condition of the probasisternum in a wide range of Asilids, concluded that too much variation occurred for it to be used as a diagnostic or even supplementary character. Hull (1962) en- dorsed this conclusion. It seems that the probasisternum was made to appear much more erratic than it really is. Several factors might have contributed towards the creation of this bewildering situation:

1. The concept of tribal and subfamily grouping recognised at that time is different from the one at present accepted; each of the Asilinae and Dasy pogoninae has been segregated into several subfamilies and many tribes have been dispersed and combined with others.

2. Students of the Asilidae had little agreement between themselves in their interpretation of the status of the probasisternum. Clements has cited several cases when his findings were contradictory to those of Hardy. On the other hand, Clements and Hull have expressed different views; the former maintained that the probasisternum is - 171 -

always narrowly bridged in Machimus, while the latter claimed that it is always dissociated. In Machimus adustus, M. atricapillus and M. notia lis, which were examined during the present study, this organ is bridged.

3. According to Clements and Hull, some genera, such as Asilus, Cerdistus and Ommatius have both bridged and dissociated probasisterna - this has been here conf/rmed for Ommatius. However, they did not indicate the proportions in which the two conditions coexisted - most probably one form would be dominant while the other exists as an anomaly.

Papavero (1973) has divided the Asilidae (excluding the Leptoga.sfcejidae) into eight subfamilies, which are the Apocleinae, Asilinae, Ommatiinae, Dasypogoninae, LapViriinae, Laphystiinae, Stenopogoninae and Trigonomiminae. His evaluation of the condition of the probasisternum is as follows:-

1. Dissociated (except one genus) in Dasypogonin*e. 2. Fused to the,proepisternum in Laphystiinae, Laphriinae and Trigonomiminae. 3. Variable in Apocleinae, Asilinae, Ommatiinae and Stenopogoninae.

In the Asilids seen the probasisternum was found to be dissociated in Apocleinae, Dasypogoninae (except Blephare- pium) and Stenopogoninae (Stichopogonini not seen). It is fused in Asilinae (Cerdistus not seen), Laphystiinae, Trigonomiminae and Laphriinae. The two conditions coexisted in Ommatius (dissociated in two species and bridged in one) .

Martin (1968) has given Leptogastjrinae separate family status and was followed by Papavero (1973). Oldroyd (1969) saw no justification for the segregation and this view was adopted by Wood (1981). The. Lepto-' gasterinae possesses a combination of characters that readily separate it from the rest of the Asilidae. .These are: - 172 -

1. The postpronotal lobes are produced forward as horn- like projections. 2. The mesonotum is so expanded anteriorly that it overlaps the antepronotum.

3. On each side of the mesoscutum, just above the basalar plate, there is a subtriangular pit (tgpt^) from beneath which a short apodeme projects into the thoracic cavity. 4. The anterior trans-scutal suture is obliterated. e 5. A character that the Leptajastjrinae shares with the Ommatiinae and Atomosiini is the expansion of the metepimeral plates to meet each other behind the metacoxae. In Leptogaterinae the two plates are separated by a narrow groove, but the fusion is complete in Ommatiinae and Atomosiini.

Some of the Asilid subfamilies are very large and comprise distinctive groups, e.g. the Stenopogoninae and Laphriinae. In the former, the probasisternum is dissociated in Stenopogonini but fused in Stichopogonini (Hull, 1962). In Laphriini the area behind the metacoxae is membranous but it is completely sclerotised in the Atomosiini. I believe that the splitting of each of these into two subfamilies would produce more manageable groups.

The prephragma shows a considerable variation both in shape and size but may still be of some taxonomic value if used in combination with other characters.

EMPIDIDAE (Figs. 65-69)

The Empididae and Dolichopodidae have long been recognised as a natural unit (Brauer, 1890). Enderlein (1935) has expressed the radical view that, together with the Lonchopteridae, they deserve subordinal rank.

The fusion of the posterior intersegmental suture - 173 -

with the metapleural suture readily separates this group from the rest of the Brachycera. However, this character does not seem to be peculiar to this group. Incidental to the present investigation, I examined a few Cyclorrhaphan specimens. In some of these, the posterior intersegmental suture is fused to the metapleural suture. Further studies may demonstrate that this phenomenon is widely distributed among the lower Cyclorrhapha. If this proves to be the case then either:-

1. Empidoidea should be removed from the Brachycera and included in the Cyclorrhapha, or alternatively

2. the Cyclorrhaphans that possess this character should be combined with the Empidoidea in a separate section or suborder (the possibility that this character might have developed independently in more than one line, though very remote, cannot be excluded).

The Empididae is separated from the Dolichopodidae by its lack of the distinctive characters that define the latter family.

The extent to which the intersegmental suture is united to the metapleural suture varies with the different Empidid genera. In Empis the .two sutures fuse in the middle, thus dividing the metanepisternum into two subequal portions. In Platypalpus and Drapetis the fusion is almost complete, while the two sutures are only fused at the ventral apex of the metanepisternum in Phyllodromia.

In Hybos, Ocydromyia a:nd Drapetis the probasisternum is separated from the proepisternum by membrane, but broadly fused in Empis, Platypalpus and Clinocera. In Phyllodromia the fore limbs are located well forwards, while the profurcal pits are situated some distance behind the posterior margins of the coxal bases. In Clinocera the probasisternum is extensively sclerotised anterior to the fore coxae. - 174 -

The prephragma is strongly bilobed in Empis, Hybos, Ocydromyia, Drapetis , Platypalpus and Phyllodromia. In Clinocera this organ is shield-shaped and lacks the lateral arms.

Collin (1961) has used the character of the probasisternum to define the Empidinae and Hybotinae (including the Ocydromyiinae), it is complete in the former but dissociated in the latter. The Clinocerinae and Hemerodromiinae are reliably defined by the characteristic shapes of their probasisterna.

Drapetis is a distinct genus and Collin (1961) placed it in a tribe on its own within the Tachydromiinae.lt differs from Platypalpus, another member of the Tachydromi'inae, in the following aspects:-

1. Drapetis has a dissociated probasisternum. This organ is complete in Platypalpus.

2. In Drapetis the postpronotal lobes are indistinguishably fused to the mesonotum. These lobes are callose and are delimited from the mesonotum by sutures in Platypalpus.

There are several- minor differences between the thoraces of the two genera, but I am using the form of the probasisternum to elevate the tribe Drapetini to subfamily status.

DOLICHOPODIDAE (Figs. 70-76)

The Dolichopodids make up a very extensive and diverse group. They possess many distinctive characters that establish them firmly as a well defined monophyletic family. Of these Ulrich (1971) refers to the following:

1. The presence in the neck region of a crescentic ventral - 175 -

cervical sclerite.

2. Each postcervicale bears an elongate, posteriorly directed internal apodeme. In all other Brachycera examined, the postcervicale is provided with a transverse ridge.

3. The presence on the mesanepisternum of an oblique, clavate, heavily pigmented area from beneath which arises an internal ridge that Ulrich calls the "mesanepisternal pad". A more dorsally situated internal ridge has been identified on this area in Apiocera, Psilocephala, Xylomya and certain Stratiomyids, but the external cuticular pig- mentation is here lacking.

4. Ut.rich considers the modification of the anterior part of the mediotergite into a convex subscutellum to be an apomorphic character of the Dolichopodidae. The occur- ence of this character in the Stratiomyidae, Syrphidae and Tachinidae has long been established ('Curran, 1924). •

5. The upper portion of the mesanepimeron that extends between the subalar fissure and the laterotergite is heavily pigmented. 6. The metapostnotum bears an internal apodeme at its ventral limit. 7. The metapleural ridge bears two rod-like internal apodemes. The present study has shown that the Asilidae possess a dorsal metapleural apodeme and that Apiocera has the ventral edge of the metapleural ridge modified into a long, spatulate arm. Ulrich has also recognised the presence of a tiny dorsal metapleural apodeme in some Empididae. However, the two metapleural apodemes are not known to occur together except in the Dolichopodidae.

8. Both the Dolichopodidae and Empididae have the posterior intersegmental suture fused to the metapleural suture .

Ulrich (1980) has divided the Dolichopodidae into ten subfamilies which are the Dolichopodinae, Diaphorinae, - 176 -

Hydrophorinae, Sympycninae (= Campsicneminae), Rhaphiinae, Neurigoninae, Medeterinae, Systeninae, Enliniinae and Sciapodinae. In previous treatments (Brues et al, 1954; Robinson, 1970) no less than 14 subfamilies have been recognised, but the contents of these differ so much that a comparison between the different subfamily concepts is almost impossible.

Ulrich's (1971) pioneering work on the thoracic morphology of Dolichopodidae has been more recently followed by the investigations of Marina & Negrobov (1977, 1980) who considered such features as the form of the sella, the shape of the probasisternum and profurcasternum, the condition of the prephragma, the shape of the meso- and metafurca and the form of the metathoracic apoderoes. One of their conclusions is that the Dolichopodinae forms a very uniform subfamily, while the Sympycninae is a very diverse one. This may indicate that the latter is an ill defined group.

After seeing the prephragma in Dolichopus,Poecilo- bothrus and Hercostomus, I had the impression that the shape of this organ is so uniform that it can be used as a subfamily character for the Dolichopodinae. However, on examining the prephragma in Tachytrechus (Dolichopodinae), which lacks the lateral arms, I abandoned this view. Among the Hydrophorinae, Liancalus and Machaerium possess a prephragma similar to that of Poecilobothrus, but in Hydro- phorus and Aphrosylus this organ is identical to that of Tachytrechus. Medetera truncorum has a characteristic prephragma that is not repeated in any of the Dolichopodids studied. The five species of Argyra examined demonstrate slight variations both in the prephragma and metafurca, with A. diaphana at one extreme and A^ vestita at the other. This suggests that either the genus is in fact an aggregate of two or more distinct genera or that these two features are too variable to have any taxonomic use in this particular case. - 177 -

The presence of a postcervical apodeme has been established by Ulrich (1971) but the potential of this feature as a diagnostic character was not explored. For a long time, a subfamily status has been maintained for Aphrosylus. Robinson (1970) combined it with the Hydro- phorinae and was followed in this by Ulrich (1980). The present study has revealed striking similarities between the prephragmata and metafurcae of Hydrophorus and Aphrosylus. The two genera could, however, be readily separated by the form of the postcervical apodeme, which is short and broad in Aphrosylus but long and thin in Hydrophorus.

It is surprising that with all the structural diversity evident in it, this family contains less than 170 genera (Ulrich, 1980). The Asilidae, which is comparable to the Dolichopodidae both in diversity and size contains more than 450 genera according to Papavero (1973). The status of many broadly based genera, such as Argyra, needs to be reconsidered in the light of the recently discovered data. - 178 -

VI DISCUSSION

It seems relevant to open this discussion by asking two questions: what do taxonomists classify and what criteria do they employ to make a classification? Henni^ (1965) and Blackwelder (1967) believed that the simplest elements of biological classification are the individuals: taxonomists first establish that different individuals belong to particular species. Species are then grouped in- to a hierarchy or ascending sequence of levels or "categories", i.e. genera, tribes etc. The criteria upon which this systematisation is based are the total set of characters by which members of one taxon differ from those of another at any pertinent level (Blackwelder, 1967; Mayr, 1969). Such features may be derived from the fields of ecology, physiology, behaviour etc. but it is customary for systematists to lay greatest stress on those obtainable from preserved specimens, i.e. morphological characters. The evaluation of this latter group of data and the assess- ment of the role they can play in the construction of classificatory schemes form the theme of the present study.

Systematists have long disregarded characters whose resemblence appears to rest on convergent evolution, but the credit for assigning special significance to the distinction between ancestral (plesiomorph) and derived (apomorph) characters is due to Hennig (1953, 1965, 1966, 1969). This author has repeatedly stressed the point that before a character state is employed in phylogenetic systematics, it is necessary to assign to it the concepts of plesiomorphy and apomorphy and that only the latter group of character states can be used to establish raono- phyletic groups and thus to estimate evolutionary relationship. The strength of this argument is self-evident; some features can remain unchanged during a number of speciation processes and therefore their possession cannot constitute evidence of close relationship of their possessors. In the Brachyceran Diptera the state of the empodium illustrates - 179 -

this argument (cf. p. 154).

Taxonomic characters usually have a dual function:-

1. They serve as indicators of relationship. In this form they are designated as "similarities" or "resemblances". Hennig (1969) is apparently the first to apply the expression "constitutive characters" to this phase.

2. They emphasise the differentiation between groups. In this condition, they are referred to as "diagnostic characters" or "differences".

When employing a set of characters, taxonomists place more confidence in certain features than in others. This is known as "weighting". There is no golden rule for judging which characters are most appropriate and at what level; a feature that may have high weight in one group may be of very low weight in another. A useful but time-consuming procedure for appraising taxonomic characters is to work backwards from a classification that produces workable groups and study the features that delimit such groups. This approach has proved very fruitful during the present investigation. No better example can be cited than the establishment of the state of the sella as a prime character in the classification of Bombyliidae. The clue that led to this has come from two different sources:

1. Traditionally the Bombyliidae is divided into two major groups; one associated with Anthrax and the other with Bombylius. This system has never been challenged (Bowden, 1980) and was here accepted as a basis for character search.

2. The interesting findings of Speight (1969) with regard to the universality of the sella in Acalypterae and his suggestion that this organ might have evolved independently of the presternum were inspiring and the result was reward- ing. It required no effort to locate the sella in all the - 180 -

Bombyliinae examined, but an examination of the area directly anterior to the probasisternum gave a negative result in the Anthracinae. The implication that the sella is absent from this group was unconvincing. After closer examination of stained specimens, I could discover the presence in the Anthracinae of a very characteristic sella displaced much forwards than is usual.

The Empidoidea has been recognised as a discrete group for nearly a century. Many larval and imaginal characters have been employed in defining its limits but the introduction of the state of the posterior intersegmental suture as one of its major constitutive characters is due to Ulrich (1971). Once discovered, this character seems so obvious it is surprising that it remained unobserved for so long.

The two preceding examples clearly demonstrate that single features can be effectively used in recognition of certain groups. Such clear-cut characters are not always available.

Very often a situation arises when a taxonomist has to deal with either a morphologically very uniform or highly diverse group. In such cases inference of relationship could only be drawn from the synthesis of several characters, which may be only few or very many. Bla.ckwelder (1967) and Mayr (1969) suggest that the number of characters used should not be more than is necessary for the establishment of a sound classification. However, both authors recommend that the investigator should extract the maximum information obtainable from the taxon examined, the data not used in making the classification are stored in the system. Hennig's main emphasis is on the derived transformational stages of characters rather than on their numbers, but he believed that the more numerous and particular the derived characters, the more certain we are that a group possessing them is monophyletic. - 181 -

A museum taxonomist usually works with preserved insects. His first task is to assemble the material before him into groups of similar samples. He then has to decide whether to assign these samples to a single species or to several. This decision forms the most fundamental step in constructing a classification because it defines the taxonomist's concept of what constitutes a species and which features are most important for defining specific limits.

For over two centuries, taxonomic species have been vaguely defined as "what competent taxonomists accept as species". This definition served to distinguish nearly a million species. In recent years, it has been described as arbitrary, inadequate and unsound. The most acclaimed alternative definition is: "Species are groups of inter- breeding populations that are reproductively isolated from other such groups" (Mayr, 1969). This definition applies to bisexual groups, but not to asexual or unisexual forms (which are not a negligible exception). For many sexually reproducing groups, the reproductive isolation mechanism cannot always be verified experimentally. Mayr (op. cit) thinks that these difficulties are not serious enough to invalidate this definition; Blackwelder (1967) suggests exactly the opposite. Hennig is silent on this point although he (Hennig, 1966, 1969) categorically states that it is only possible to speak of phylogenetic relationship in sexually reproducing animals. Blackwelder, Mayr and Hennig are the chief proponents of three approaches to systematics, which are usually referred to as "formal systematics", "evolutionary systematics" and "phylogenetic systematics", respectively. In practice, adherents of the three systems use morphological differences to delimit species against'" each other, but their reasoning is not the same: evolution- ists and phylogenticists regard species as 'reproductive communities that are genetically and not morphologically defined; they consider morphological differences as evidence from which they infer the existence of reproductive isolation or genetic discontinuity, while these differences provide - 182 -

the basis on which formal species are distinguished (Mayr, 1969).

According to Blackwelder (1967), species are arranged into higher categories on the basis of shared characters. Hennig (1965 and later) states that grouping ought to be based on shared derived characters and not shared ancestral ones. Mayr (1969) points out that the principal factors that influence the use of characters for any taxonomic purpose are:-

1. Complexity; complex characters are given higher weight because the possibility that they have become similar by convergence is very low.

2. Consistency; features that are consistently present in members of one group and consistently absent in members of related groups are more reliable than those that occur sporadically and merely vary in the frequency of their occurrence.

3. Correlation; characters that are believed to be phylo- genetically correlated are given more weight than function- ally correlated ones. The distinction between the two kinds of correlations is highly subjective. But it seems legitimate to assume that most character changes have a functional basis. Some of the modifications become stabil- ised and eventually incorporated into the genetic heritage, while others remain variable. The haltere is an example of the former and the mouth parts exemplify the latter category. This is an oversimplification of facts but I hope it would provide a basis for useful discussion.

The value of Hennig's dictum about the necessity of dividing character states into ancestral and derived phases does not need to be emphasised. Even if a character satis- fies the three requirements mentioned above, its significance cannot be properly judged without predicting its possible - 183 -

V evolutionary history. Like all other man-made rules, this useful yardstick has often been twisted to fit a particular situation and in one case this was done by Hennig himself. Prior to 1965, Hennig considered the pulvilliform empodium to be an ancestral character. Ross (1965) put forward the view that the pad-like empodium is a derived character of the Homoeodactyla. Hennig (1969) grasped this suggestion and later (Hennig, 1973) broadened the concept of Homoeo- dactyla to contain the Nemestrinoidea (including the Bomby- liidae)! One of the axiomatic assumptions on which the Hennigian phylogenetic systematics is based is that a character should demonstrate a minimum of two states, an ancestral, and a derived phase. An obvious implication of Hennig's view is that the absence of the fleshy empodium represents the ancestral stage. Quoting Hennig (1965, p.107): "The possession of at least one derivative (relatively apomorph) ground plan character is a precondition for a group to be recognised at all as a monophyletic group. But it also follows from this that this same character in the nearest related group must be present in a more primitive (relatively plesiomorph) stage of expression". This "precondition" is not met in the case of the pulvilliform empodium. I have already pointed out that the fate of the empodium in the HETERODACTYLA sensu Hennig is obscure (p. 155). If we apply Hennig's definitions we find that the HOMOEODACTYLA sensu Hennig (1969) is a paraphyletic group because it excludes the Nemestrinidae, while the HOMOEODACTYLA sensu Hennig (1973) is polyphyletic because it includes the Bombyliidae.

The pretence to comply with phylogenetic rules is often very frustrating and phylogeneticists are prone to this weakness; Speight (1969) has mentioned that many of Hennig's Acalypterate families are based on plesiomorphic characteristics. It seems that .the sheer weight of a clear-cut character forces it into use despite what rules say. I suspect that this is why the pulvilliform empodium remained as a thorn in the flesh of dipterists for nearly a century. I quest- ioned the validity of Ulrich's (1971) claim that the fusion \ - 184 -

of the posterior intersegmental suture is an apomorphic character of the Empidoidea (p. 173). But I must admit that this feature alone dictates that the Dolichopodidae and Empididae should always remain close to each other.

The sella provides a suitable example of a feature for which a reasonably reliable evolutionary sequence can be constructed; its evolution from a poorly differentiated structure carrying a pair of loose bundles of sensilla into a highly complex organ bearing two compact sensillar plates could easily be followed through all its developmental stages. The Tabanidae and Stratiomyidae have a weakly differentiated sella. In Pantophthalmus and Chrysopilus the sella is present as a well defined attenuated plate but the sensilla are still more or less loose.

Starting from this point both the anterior and posterior part of the sella are involved in a series of modifications that are difficult to explain in terms of a lin- ear sequence. For simplicity I will assume that the transformations undergone by the anterior portion occur independently of those taking place in the posterior part. Let us first examine the sensilla-bearing anterior part of the sella and see whether it has a role to play as a taxonomic character.

If the form of the sella in which the sensilla occur as two loose bundles is considered to be the more ancestral phase, and that where the sensilla are present as two tight bundles to represent the more derived stage, then the Brachy- cera can easily be divided into a lower and a higher group; members of the former group demonstrate the more primitive phase while those of the latter possess the more derived one. Rhagio is arbitrarily regarded as standing on the dividing line. The lower Brachycera as interpreted here consists of the Tabanidae, Pelecorhynchidae, Pantophthalmidae, Stratiomyidae, Xylomyidae, Xylophagidae and Coenomyidae. The Rhagionidae, even after the separation of Vermileonidae, is still ill defined and cannot be referred to as a discrete - 185 -

group. The only generalisation that can be made here is that Rhagio and its allies belong in the lower Brachycera, at least as far as the sella is concerned.

In almost all classificatory schemes suggested for the lower Brachycera attempts have been made to establish some kind of relationship between the minor families of the group. Hennig (1973) placed these families under the umbrella of a single superfamily, i.e. the Xylophagoidea. Oldroyd (1964) took a different approach: he first established a close relationship between the larvae of Xylomya and Xylophagus, then he used some imaginal characteristics to relate Xylomya to Stratiomyidae and Xylophagus to Rhagionidae. He further extended this argument to suggest a link between Stratiomyidae and Rhagionidae. I feel that Oldroyd's loosely knitted chain of relationship is better founded than the bold decision taken by Hennig. The only character that suggests the exclusion of Xylomya from Stratiomyidae is the wing ventation; if this difference is overlooked Xylomya can be absorbed in the Stratiomyidae and HennigTs superfamily will be shattered:: The position of Coenomyia is obscure. It is the only genus outside the Stratiomyidae that possesses scutellar spines. These structures might have been acquired independently in the two groups and so cannot suggest a special relationship.

An unsettled point in this area is the relationship between the three major families, namely the Tabanidae, Stratiomyidae and Rhagionidae. The strongly convex, pear- shaped sella of the Tabanidae is not seen elsewhere in the Brachycera, not even in Pelecorhynchus, which once belonged in it. Both in the form of the sella and shape of the probasisternum Pelecorhynchus has a closer resemblance to Atherix than to any of the Tabanids seen. Pantophthalmus has a sella similar to that of Chrysopilus, while its probasisternum resembles that of Coenomyia. This may suggest that the Tabanidae is more isolated from either of the other two families than are these from each other. However, the wing venation and the alleged habit of sucking blood - 186 -

place the Rhagionidae nearer to the Tabanidae than to the Stratiomyidae. On the other hand the antennal segmentation indicates that the Rhagionidae is a much more derived family than either the Tabanidae or Stratiomyidae.

In the higher Brachycera (according to the present concept) the development of the sella seems to have followed different evolutionary pathways. In all groups that I consider to belong here, the sensilla are borne on a pair of compact plates, but the shape of the area carrying these plates is rather variable. In the Anthracinae this area is greatly attenuated anteriorly. In the Asilidae the compact sensillar bundles are borne on two isolated plates that lie at the anterior margin of a raised membranous area. These are examples of high specialisation. In its relatively plesiomorphous stage (within the higher Brachy- cera) the anterior part of the sella is more or less rounded in shape, as is seen in the Bombyliinae, Therevidae and Empididae.

In most of the higher Brachycera the posterior part of the sella tapers posteriorly. This portion could be considered to exist in the plesiomorphic stage when it is short and the apomorphic phase when it is modified into a long median bar. In the Dolichopodidae the posterior part of the sella is present as a more or less broad plate that is almost completely separated from the anterior part by a medial constriction. Marina and Negrobov (1977) have demonstrated that some Dolichopodids possess a sella of a characteristic shape that could help to define some subfamilies, e.g. Sciapodinae and Medeterinae.

The posterior part of the sella tapers into a long median bar in Therevidae, Apiocera and Empididae. A detailed study of the sella, such as counting the number of sensilla borne on each plate may throw more light on the evolutionary patterns of this organ and help in the construction of an effective hierarchy for the Brachycera. - 187 -

It should be mentioned in passing that many thoracic structures suggest that the Brachycera are divisible into three groups: the Scenopinidae, Empididae and Dolichopod- idae share many similarities with the Stratiomyidae, the Nemestrinidae and, to less extent, Bombyliinae recall the Tabanidae, while the Therevidae, Asilidae, Apiocera and Hilarimorpha resemble the Rhagionidae. The Acroceridae can be included in the Tabanid line on the basis of the similarities it shares with the Nemestriniade. The Mydids stand on their own.

From an examination of the state of the probasisternum, whether it is united to the proepisternum or separated from it by membrane, I found that both conditions exist in the Tabanidae, Asilidae, Empididae and Anthracinae. In all the Therevidae, Mydidae, Stratiomyidae, Dolichopodidae and in Xylomya it is united. It is also united in Pantophthalmus but its visual shape here is very peculiar and not comparable to any other fused form within the Brachycera. The most that can be said here is that it may be derived from the dissociated probasisternum of Coenomyia. The probasisternum is dissociated in Rhagionidae, Nemestrinidae, Bombyliinae, Pelecorhynchus, Hilarimorpha and Apiocera. It is very narrowly united in Ogcodes but dissociated in the other Acrocerids seen. In both Xylophagus and Coenomyia the probasisternum continues laterally anterior to the coxa (on each side) to taper in a finger-like structure that does not reach the proepisternum. This character indicates a close relationship between the two genera.

After the severe criticism directed to Hardy's (1948) views about the taxonomic value of the probasisternum, this organ received scant attention from taxonomists working on the Brachycera. I have shown that Clements' argument is no longer valid. It is worth noting that the line of cleavage between Asilinae and Apocleinae coincides with the state of the probasisternum, the members of the former group predominantly demonstrate a fused probasisternum while those of the latter possess a dissociated one. - 188 -

The distinction between the ancestral and derived form of the probasisternum has, in the first place, been conditioned by a preconception about the relationship between the Tabanid subfamilies Pangoninae and Tabaninae. In order to keep in tune with a widely accepted view that these two subfamilies are very distinct, I assumed that the dissociated probasisternum is relatively more ancestral than the fused one. Consequently it was found possible to regard all the Tabanid species that possess a fused probasisternum as constituting a monophyletic group. These were combined under the subfamily Chrysopsinae. The only possible change that may result from this suggestion is the transfer of the Scepsidini from the Pangoninae to the Chrysopsinae. In both the Asilidae and Empididae the condition of the probasisternum cannot be used as a primary subfamily character. But it could be said in retrospect that subfamilies in both groups tend to contain species in which the probasisternum is either predominantly fused or dissociated. The significance of the state of the probasisternum within the Anthracinae sensu lato is yet to be assessed. Among the genera seen, the probasisternum is fused in Anthrax, Spogostylum, Tomomyza and Antonia, while it is dissociated in Exjjprosopa and allies and in Lomatia. In any future reorganisation of the A Anthracinae the probasisternum must not be overlooked.

Nothing needs to be said about the tergal apodeme except that Mickoleit's (1969) claim that it is an apomorphic character of the Brachycera is not acceptable. This organ is associated with one of the important flight muscles. As long as this muscle (the posterior basalar muscle) is functional, the apodeme, or its homologue, must be present. This structure is greatly reduced in the Acroceridae and Nemestrinidae and is indiscernible in the Mydidae. The flight mechanism in these families seems to be highly modified in order to meet specific requirements~- This is especially true of the Mydidae.

Several specialised characters have been noted, some at the family level, others at more subordinate levels. - 189 -

In the former category are the ventral cervical sclerite and the postcervical apodeme in Dolichopodidae, the postphragmal ridges in Nemestrinidae and the tergal fulcrum in Bombyliidae. Among the latter group are the confluent profurcal pits and the spinasternum in Systropus.

The occurrence of unique characters inevitably raises the question of ranking. If a taxon possesses a clear- cut character that is absent from its nearest relatives its position in the hierarchy should reflect this fact; otherwise the classificatory system would be cluttered with unnecessary exceptions. The following examples may illu- strate this:-

1. I have noted the presence in Liancalus virens (Dolichopodidae) of a well developed, posteriorly directed proepimeral spine that arises near the posterodorsal margin of the coxal base. If further studies show that this spine is present in all species included in Liancalus, it would be one of the many diagnostic characters of this genus and should not warrant any special consideration. If it is consistently present in some species and equally consistently absent from others, then only one of the two clusters of species could be retained in Liancalus while a new genus should be erected for the other group (if a genus is not already available).

2. Systropus and Toxophora are very characteristic Bombyliid genera. In fact they are so distinct that the only feature which made their inclusion in the Bombyliidae possible is the wing venation (it has been shown in the present study that the tergal fulcrum is another constitutive character that confirms the correctness of this placement). The two genera and allies have enjoyed different hierarchical status within the Bombyliidae; Bezzi (1924) treated them as two subfamilies while Bowden (1980), although he thought they deserve full family status, has combined them in one subfamily. The newly discovered characters reported in this study bring to the fore the - 190 -

whole question of the systematics of Bombyliidae. There are two sets of characters that can be employed to divide the family into two groups:- a. The characters that distinguish the Systropus complex (Systropus + Toxophora) from the rest of the family. b. The characters that set apart the Anthracinae as a distinct group.

The decision to subordinate one of these sets of characters to the other is highly subjective and is difficult to take because it eventually affects the rank of one of the groups resulting from it: if set (a) is used first the Systropus complex will be assigned to the same hierarchical category as the combined Anthracinae/Bombyliinae group. If set (b) is employed as the prime set, the Systropus complex will form a subunit of the Bombyliinae sensu lato. One factor that may influence the "ranking" of characters is a consideration of the nature of the groups created. In one case, the two groups will be very unequal. If the other alternative is followed, the family will be divided into two comparable groups, at least as far as the size is concerned. My own view is that dis- tinctness should be given priority over other considerat- ions .

It is a fact of life that most animal groups exist as readily recognisable and definable natural units. The Insecta qualifies as such. Despite this fact, the entomological literature abouncfs with so many controversies over the naturalness or artificiality of observed phenomena that the casual reader may have the impression that the contention is over an abstract issue and not concerned with discrete entities that have a real existence in nature. This is mainly because there are too many theories put forward to explain too few known facts. The one branch of entomology that suffers most of this is "systematics". If this branch continued to be known simply as systematics - 191 -

without any connotative qualifications and if systematists continued to have as their sole aim the discovery of diversity of species much of the dispute between them could be avoided and the time wasted in discussing peripheral issues would have been better employed, Hennig's (1965) statement that "... whether ... systematics will, in future always try to express the morphological resemblance of organisms or their phylogenetic relationship" leaves no room for compromises.

If I confine myself to the Brachycera, I find that major subgroups are based on structural similarities, Hennigf s HOMOEODACTYLA is no exception. I failed to see any evidence that indicates the involvement of the time sequence of branching in the classification of this group. Phylogeneticists would contend that these similarities are the product of branching: similarities are part of the heritage passed on by the stem group to its daughter groups and the argument becomes circular.

The few features that I regarded as group characters, such as the characteristic sella in both Anthracinae and Asilidae, and the postphragmal ridges in Nemestrinidae, indicate that it is the presence of the character that is important, and not the hypothetical phylogeny that would justify its use in taxonomy. If the reverse is claimed then systematists must put down their pens and wait in anticipation for someone who would one day come and say "Eureka, this is how life began and how it has evolved". t - 192 -

SUMMARY

In the preceding sections, the results have been out- lined of a morphological study based on a limited number of species, and in most cases no more than a couple of specimens has been seen from each species. Despite these limit- ations, a few interesting points have been brought to light, the more important of which are mentioned below:-

1. One of the most striking characters examined in this investigation is the sella. This organ has been mistaken for the presternum, which is assumed to be a detached part of the probasisternum. Speight (1969) has clarified this point for the Acalypterate Diptera and the present study has shown that, within the Brachycera, the sella has evolved from a poorly differentiated structure into a very complex organ that does not owe its origin to the probasisternum. It has been suggested that this feature can be used as a diagnostic character to divide the Brachycera into a lower and higher group, as a constitutive character to establish both the Asilidae and Anthracinae as monophyletic groups and to define some subordinate groups within the Dolichopodidae and Bombyliinae sensu lato. Further detailed studies on this organ are still badly needed.

2. The potential for the probasisternum as a taxonomic character has been assessed. Using this feature as a major criterion of classification, I have tentatively combined all Tabanid species with a united probasisternum under the enlarged subfamily Chrysopsinae. I have also used the condition of the probasisternum to divide the Empidid Tachy- dromiinae into two subfamilies, i.e. Tachydromiinae sensu stricto, in which the probasisternum is united to the proepisternum and the Drapetinae in which this organ is dissociated. The Empidid Trichopeza longicornis, which is regarded as a member of the Clinocerinae, has a dissociated probasisternum, which allies it to the Hybotinae/Ocydio- myiinae group. It has been suggested that the use of the - 193 -

probasisternum in the classification of Asilidae should be reexamined.

3. Several unusual characteristics have been reported for the first time. Among these are the tergal fulcrum in the Bombyliidae, the postphragmal ridges in the Nemestrinidae, the confluent profurcal pits and the presence of a spinasternum in Systropus and the mesanepisternal pad in certain Stratiomyidae and in Xylomya.

4. Some genera possess a prephragma of a characteristic shape and in few cases, as in some Asilidae and Stratiomyidae, the prephragmal shape shows a specific pattern for a whole subfamily. I have pointed out that the prephragmal variation within Bombylius suggests that this genus is possibly an aggregate of two or more distinct genera.

5. The existence of two independent terminologies,i.e. a morphological and descriptive one, has burdened the entomological literature with an inhibiting array of terms in which either different names are applied to the same structure or the same name applied to different structures. As a result of a critical search of the literature, it was possible to adopt a uniform and consistent nomenclature that is applicable throughout the Diptera.

6. A detailed comparative study of the thoracic morphology of a considerable number of Brachyceran species, including both generalised and highly modified forms, has helped to clarify many disputed points about the identity and homology of several thoracic structures, such as the prescutum and preepisternum.

7. A few familiar terms, such as the presternum and precoxale, have been rejected on the ground that they do not define discrete morphological structures that have an independent existence.

8. It has been found that the major families of Brachycera, - 194 -

except Rhagionidae, form well defined morphological units, but the anomalous genera that fit near the base of the group cannot easily be united into larger units.

9. It has been suggested that current opinions regarding interfamily relationships are based on insufficient data. - 195 -

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