THE GEOLOGICAL MAGAZINE.

No. C—OCTOBER, 1872.

AETICLES.

I.—NOTES ON SOME BRITISH PALEOZOIC CRUSTACEA BELONGING TO THE ORDER MEBOSTOMATA. By HENRY "WOODWAKD, F.G.S., F.Z.S.; of the British Museum. ' (PLATE X.) On the Hemiaspis, H. Woodw., 1865.1 Species 1.—Hemisaspis limuloides, H. Woodw., PI. X., Figs. 1 and 2. When I first drew attention to this genus at the Bath Meeting of the British Association in 1864, only one nearly perfect speci- men was known. Mr. Salter was acquainted with this form, so long ago as 1857, and referred to it, among other new and undescribed Crustacea, in a paper "On some New Palaeozoic Star-fishes" found at Leintwardine, Shropshire,2 under the name of Limuloides. Portions of several others had also been met with, to which Mr. Salter attached MS. names in (the Museum of Practical Geology, Jermyn-street, but they have not been heretofore described. The most perfect of these Limuloid forms was described by me in a paper read before the Geological Society in June, 1865.8 (See Plate X. Fig. 1.) Since that date other fragments have been found, and also another nearly perfect example (obtained by the late Mr. Henry Wyatt-Edgell) of the form named by me Hemiaspis limuloides, which, having the upper central portion of the carapace preserved, nearly completes our knowledge of this species. (See PL X. Fig. 2.) The great interest attaching to this form arises from the fact that it offers just the desiderated link by which to connect the XIPHOSURA with the EUBYPTERIDA. Limuli, apparently differing but little as regards their carapace from the recent species now found living on the coasts of China, Japan, and the north-east coast of North America, occur as early as the deposition of the Solenhofen Limestone of Bavaria : and in the Coal-measures of England and Ireland several species of Bellinuri and Presticichice occur, in which behind the cephalic shield the body is composed of five more or less free thoracic segments, and the rudimentary abdomen, if not anchylosed in all, is so in most. (See Plate X. Figs. 8, 9, and 10.) 1 Extracted from the Author's Memoir on the Merostomata, Part iv. p 174 Pal. Soc. Mon.,T0l. for 1872. 2 See Ann. and Mag. Nat. Hist., 2nd series, vol. xx., 1857, p. 321. 3 See Quart. Journ. Geol. Soe., 1865, vol. xxi., p. 490, pi. xiv., fig. 7. VOL. IX.— NO. O. 28 434 H. Woodward—Notes on Palceozoic Crustacea.

But in the specimen under consideration we have the eephalic, thoracic and abdominal divisions still remaining distinct, and ap- parently capable of separate flexure. This important character at once separates it from Limulug, Bellinurus, and JPre»twichia. I have 1 on this account not used the MS. name of Limuloides as a % generic appellationpp , but have proposepp d the name Hemiaspis (from 1 jfi, half, and dhdcnrh, a shield), reservini g thh e MSMS . name Limu-Li hides for the specific title of the most perfect species of the genus. (See Plate X., Figs. 1, 2.) But it will be observed that Hemiaspis is also, in general appearance, strongly severed from the other species of Eurypterida, as well as from the Xiphosura, in structure. The three divisions into head, thorax, and abdomen are more strongly marked. The abdomen is reduced to very slender pro- portions, less than one-third the length of the (the entire specimen measuring 2J inches in length by one inch in width). The carapace in general outline resembles Limulus, but is more dilated laterally. There is a small stellate ornamentation in the centre of each cheek, having five to six rays, and measuring about a line in extent; but whether this represents the position of the eyes I am quite unable to say. It is unlike the eye of any other member of the group, which causes me to doubt its relation to that organ. It seems more probable that the eyes were placed along the lateral margin of the glabella, not upon the centre of the cheek. There is a faint indication on one side of Fig. 1 and on Fig. 2 of a facial suture to the head-shield (as in the Trilobites), with a small aperture upon its border, which may -possibly indicate the true posi- tion of the eye, but it is by no means clearly defined. The surface of the glabella when perfect (as in Plate X) Fig. 2) appears to have been almost smooth,2 save that it is traversed by two ridges which, commencing as raised tubercles on the posterior border of the head-shield, three lines apart, gradually converge and unite, so as to form an arch, the summit of which nearly touches the front border of the glabella. Nine ray-like corrugations descend from the glabella towards the margin of the shield, and the whole surface of the carapace is very minutely granulated. The head-shield is armed, on each side, near the rounded posterior angles, with two principal spines directed backwards, whilst a fringe of lesser ones ornaments each lateral genal border. The thorax is composed of six strongly trilobed plates, the epimera being equal in breadth to the central portion of each segment. The first segment is the largest, being 1 line in depth and 1\ in breadth, including the epimera, which are pointed at their extremi- 1 With the concurrence of Mr. Salter given at the time. J In the original description of the glabella of Hemiaspis limuhides (see Quart. Journ. Geol Soc, 1865, vol. xxi. p. 490) I have described the glabella from a detached portion, " as ornamented with a semicircle of nine tubercles, and a tenth immediately •within the circle upon the elevated front, and two small tubercles at the posterior margin." The acquisition of the second specimen (Plate X. Fig. 2) proves this fragment to belong to another species, not to M. limuloides, as formerly supposed. H. Woodward—Notes on Paleeozoic Crustacea* 435. ties, and slightly overlap the folio-wing segment. Thefour following segments have the borders of their epimeral pieces rounded, and gradually decrease in breadth downwards from & lines to. 7, and increase in depth from $ line to 1 line. A section of one of the segments would present an outline like that of Phacops- among the Trilobites, namely, a triple corrugation. The 6th thoracic segment is more strongly arched than- the preced- ing ones, and the lateral borders are divided into two rounded lobes on each side; breadth 5 lines, depth 1 line, Th& abdomen consists of only three segments, each 2 lines in breadth, and 1^ line in depth., The first has no epimera, and appearpp s to move freely at its articulation with the last thoracic segment. The second and third segments have small epimeral pieces, which are bilobed, with, the posterior lobes more pointed. A line of small tubercles runs down the centre of these three- joints, which are somewhat raised at their articular borders. The telson is 12 lines in length' and li- line in breadth where it articulates with the abdomen; it tapers gradually to a fine point.. If we regard the first six body- rings from the head as thoracic^ and the remaining three segments, FMK, 1. —Semiaspis Iknaloides, H. Wootf- as abdominal, we must presume ward,L. Ludlow, Leintwardine. h, the head; th, the six thoracic segments; that each of these latter is a ab, the three abdominal somites; t, the telsoa. double segment, as compared with the segments of the Ewypterida proper. On the other hand, the presence of these three segments precludes our considering the head to be the cephalothorax and the succeeding segments the abdomen, a view controverted by me in my p^aper on the structure of the Xiphosura.1 The smallness of the abdomen, and its reduction from the assumed normal number of six to three segments, seems to indicate a form by which, with the help of others, we may bridge over the interval that has heretofore existed between these two groups, the Eurypterida and the Xiphosura. Although Hemiaspis is the only genus met with in Britain having this remarkable form, we know of three Eussian genera which pre- sent almost identical peculiarities of structure. Dr. J. Meszkowski has described two forms from the Upper of the Island of 1 See Quart. Journ. Geol. Soc, 1867, vol. xxiii. p. 28, plates i. and ii. 436 H. Woodward—Notes on PalcBozoic Crustacea,

Oesel, namely, Tseudoniscus aculeatus (Woodcut, Fig. 2), and Exapinurus Schrenkii (Woodcut, Fig. 3) ; and Prof. Eichwald has described a third form under the name of Bunodes lunula (Woodcut, Fig. 4) from the same rich locality and formation.1 FIG. 2. FIG. 3. FIG. i.

FIG. 2:—Pseudoniscus aculeatus, Nieezk. \ FIG. 3.—Exapinwus Schrenkii, Nieszk. [ All from the U. Silurian I. of Oesel, Baltic. FIG. 4.— Bunodes lunula," Eichw. ) All these forms show three well-marked divisions to their bodies, namely, head, thorax, and abdomen, and all (save Bunodes) possessed a telson, or tail-spine, and free articulated thracic somites. In addition to Hemiaspis limuloides, already described, there are certain other specimens in the Museum of Practical Geology, to which Mr. Salter has appended MS. names, namely— Hemiaspis (Limuloides) speratus, Salter, MS. „ „ optatus, „ „ „ tuberculatus, ,; In Lowry's chart of the genera of Crustacea designed by Mr. J. W. Salter and myself, Mr. Salter has figured a head-shield of Hemiaspis under the name of H. Salweyi. There can be no doubt that this form is identical with Limuloides tuberculatus of Salter. I consider his Limuloides speratus and L. optatus to represent but one species, closely allied to H. limuloides. A portion of the head-shield of another form distinct from the foregoing, from the Wenlock shale, Dudley, completes the known species of Hemiaspis. Species 2.—Hemiaspis speratus, Salter, MS. sp., Plate X. Figs. 5 and 7. This species is represented by four head-shields only; the body-segments are not known. Limuloides optatus, Salter, MS., is not specifically distinct from L. speratus of Salter, and is conse- quently not retained. It is no doubt closely related to H. limuloides already described, but the carapace is broader in proportion to its length, and the radiating lines or ridges which in that species take their rise around 1 ' Archiv fur die Naturk. Livonia, Esthonia, und Kurlands,' erste serie, zweiter bd., tab. ii. figs. 12, 13, and 15, pp. 378-382. (Dorpat, 1859.) 8vo. 2 It is just possible that Bunodes may prove to be an Arachnid related to Scudder's Architarbus rotundatus fromIllinois , U.S., and A. subovalis, H. Woodward (see GEOL. MAG., 1872, Vol. IX., September number, p. 385, PI. IX. Figs. 1 and 2). H. Woodward—Notes on Palceozoic Crustacea. 437 the margin of a well-defined central glabella, in E. speratus extend over the whole surface, save a small quadrate area at the centre of the posterior border. From this small area seven diverging costse are given oif: the three in front being nearly equidistant and straight, the two next, which rise from the outer angles of the central area, divide and form a Y- FIG. 5.—Head-shield of Hemiaspis speratus, Salter, MS. Nat. size. shaped ridge on each latero-anterior (Restored.) e, probable position of border; the two most posterior costas the eye. curve upwards and outwards from the posterior border of the glabella to the lateral margins of the shield, and are marked midway by a minute lenticular space, which prob- ably indicates the position of the eye (see Woodcut, Fig. 5, e). The head-shield is broadly-arcuate in front, and the margin, especially on the cheeks, is fringed with a closely set row of minute spines ; the lateral angles of the shield are truncated, not produced posteriorly ; the hinder border of the head-shield is armed with four equidistant spines. The surface of the carapace, especially around the border, is covered with a very minute granular ornamentation. The following measurements show the relative size of the head- shields of Hemiaspis speratus: Breadth. Length. 15 lines 74 lines (Plate X. Fig. 7), Mus. Brit. 10J „ 6 „ ( „ Fig. 5) . „ 13 „ 9 „ Mus. Pract. Geol.

* * »> ^ ' » tt » This species is found in the Lower Ludlow Eock of Leintwardine, and is represented by specimens of the head only, preserved in the British Museum, and in the Museum of Practical Geology, Jermyn Street. Species 3.—Hemiaspis horridus, H. Woodw., Plate X. Fig. 6. This species, represented by a single example obtained by Charles Ketley, Esq., from the Tunnel shale, Dudley, and now preserved in the British Museum, is the oldest example in^time of this curious genus. When entire the carapace must have measured \\ inch in breadth by 8 lines in length; the edge is thickly set with prominent sharp- pointed spines ^ a line to a line^in length, whilst two strong spines, 2 lines in length, project from each posterior angle of the carapace; the spines along the hinder border of the shield, if present in this species, are not preserved in this example. The median line of the carapace, which FIG. 6.—Head-shield of Hemiaspis is slightly tumid, is marked by one horridus, H. Woodward. (Restored.) Wenlock shale Tunnel, Dudley. rounded and prominent tubercle and two elongated confluent ones, whilst on either side of this median line three other divergent lines of 438 H. Woodward—Notes on Palceozoic Crustacea. elongated tubercles arise and radiate outwards to the border of the shield. The surface of the carapace between the tubercles is finely granulated, with here and there a slightly larger pimple upon its surfaoe. Eyes not visible. There are some other fragments which, may indicate another species (see Plate X. Fig. 3), but they are too fragmentary for deter- mination, and I therefore think it -best merely to notice them in passing. Formation.—Wenlock shale, Dudley. The specimen is preserved in the British Museum. Species 4.—Hemiaspis Salweyi,1 Salter, Plate X. Fig. 4. This species is represented by two head-shields only; the body- segments, like those of the preceding species, are not preserved. The carapace, which Is very tumid, is nearly circular in outline, and mea- sures 1J inches in breadth and 1 inch in length. The posterior border ' of the glabella is armed with two large spines, 3 lines in length and 4 lines apart, whilstthree smaller ones, also directed backwards, are ar- ranged' on either side of the genal border. The surface of the cara- pace is covered with a minute gran- ular ornamentation; the raised cen- tral portion is flanked by a border of somewhat elongated -tubercles; within the central area are three or Pie. 7.—Heaa-shieia 1J-Lndlow' two oblique rows about four lines apart, commencing on the posterior border of the head at thefcase of the two large spines; one central prominent tubercle and two lesser lateral ones on the front of the glabella, complete the ornamentation of the head-shield. The spot marked e -on the subjoined Woodcut (Fig. 7), near the latero-anterior border of the raised glabella, probably indicates the position of the eye. There is a slight indication of costae on the front border of the head. Formation ;—Upper Ludlow, near Ludlow (Mus. Pract. {Jeolqgy, Jermyn St.) ; Lower Ludlow, Ledbury (British Museum).

Sub-order XIPHOSTOA, Gronovan, 1764. Genus Bdlmwnu"'Kb\ag. The name Bellinurus* was applied "by Mr. Charles Konig, in 1820,* to a «ma]l form of Limulus from the Coal-measure Iron- stone of 'Coalbrook Dale, Shropshire. The fossil was, however, .unaccompanied by any description. Another specimen of the same 1 Hemiaspis Salweyi, Salter, 1865. Lowry's Chart of Fossil Crustacea. 2 From /3eAos a dart, and oipb the tail. 3 Kbnig, Icones Fossilium Sectiles, Centuria Secunda, pi. xviii,, fig. 230. ^London, 1S20.) H. Woodward—Notes on Palceozoic Crustacea. 439

species, also from this classical locality, is figured in Buckland's Bridgewater Treatise in 1836,1 under the name of IAmulus trilobitoides. In a paper contributed to the " Annals and Magazine of Natural History" for February, 1863, vol. xi., p. 107, Mr. William Hellier Baily, F.G.S., gives an interesting account of the fossil Limuli, and defines Konig's genus Bellinurus bellulus, so that we may for. the future adopt that name as the earliest.2 Mr. Baily thus defines Bellinurus bellulus, Eonig: " General form suborbicular. Head or cephalic shield semicircular, slightly arched; the central portion (or glabella) prominent and declining towards the circumference, sur- rounded with a flattened margin, and terminating at its posterior angles in long spines. Body3 composed of fivw segments, which terminate in spines and diminish gradually towards the posterior extremity. Tail,4 or caudal portion, small, with a few slight radi- ating divisions, to which is articulated an elongated spine (telson)." Mr. Baily describes two new species of Bellinurus in his paper, namely:-— Bellinurus regina, Baily, Coal M., Bilboa Colliery, Queen's Co., Ireland. Bellinurus arcuatus, Baily, Coal M. (loc* cit.) In a communication made by me to the Geological Society iA 1867, on the structure of the Xiphosura, already cited, I proposed to retain those forms of palaeozoic Limuli with free and movable thoracic somites, and anchylosed abdominal ones, in the genus Belli- nurus, and I referred those in which all the segments appeared to be anchylosed, namely (Limulus) anthrax, and (L.) rotundata, to the genus PrestwicMa. In all these species the body consists of a head-shield, five free, or anchylosed, thoracic segments, and three anchylosed abdominal ones. I have now to record two new forms of Limuli from the English Coal-measures. 1. Bellinurus K&nigianus, H. Woodward, sj>. nov., PI. X., Fig. 8. This new form was obtained from the Dudley Coal-field, and is quite distinct from the type-species B. bellulus, Konig. The angles of the carapace are blunt, and not produced into long spines, and the five free thoracic somites terminate in obtuse serrations, not in recurved spines, as in B. bellulus. The thorax also is relatively broader in proportion to the head; the axis of the body is strongly arched and nearly straight, and does not diminish gradually towards the posterior extremity, as in the other species, although the pleurae- themselves contract to half Jheir breadth from the first to the fifth segment. The raised circular border of the glabella is not so dis^ 1 Bridgewater Treatise on Geology an dMineralogy, TOI. L, p. 396 ; vol. ii., p. 77» pi. 46", fig.3 . 3 Buckland's Limulus trilobitoides (1836), in consequence, becomes a synonym, ef Konig's Bellinurus bellulus (1820). 3 Defined by the writer as the Thoracic series of segments. 4 The rudimentary Abdominal segments coalesced. See memoir " On, some points in the structure of the Xiphosura, having reference to their relationship.,with the Eurypterida," by H. Woodward, Quart. Journ. Geol. Soc, 1867,. VjoX.xxiii), P- 28j pi. i. and ii. 440 H. Woodivard—Notes on Palmozoic Crustacea. tinctly defined as in B. bellulus, but the central axis is more strongly marked. The eyes are not very well seen, but they occupy the same relative position on the margin of the raised glabella as in B. bellulus. The abdominal division consists, as in the other species, of three coalesced segments, which are however only indicated by three marginal serrations. The tail-spine (telson) is not preserved, but its articulation with the abdomen is strongly marked. Greatest length of entire body, 9 lines. ' Greatest breadth of head-shield, 1 inch. Length of five free thoracic segments, 3 lines. Breadth of first free thoracic segment, 10 lines. Breadth of fifth free thoracic segment, 5 lines. Breadth of central axis of body-segments, 2-J lines. I have named this species after Mr. Charles Konig, the original founder of the genus, and for many years the Keeper of the Geo- logical and Mineralogical Collections in the British Museum. The original specimen is preserved in the British Museum, and was obtained by C. Ketley, Esq., from the Dudley Coalfield. 2. Prestwichia Birtwelli, H. Woodw., sp. nov., PI. X., Figs. 9 and 10. For a knowledge of this small but well-marked and very charac- teristic species of Coal Limulus I am indebted to Mr. Thomas Birtwell, of Gawthorpe Gardens, Padiham, Lancashire, who obtained it from the Coal-Measures at the Cornfield Pit on the south bank of the River Calder, near Padiham. It was from this pit that the new Arachnide (Architarbus subovalis, H. Woodw.) described in our last Number, p. 385, was obtained by Mr. Birtwell. This new species (of which there are two examples, both figured in our Plate) exhibits the most complete anchylosis of its body- segments of any of the Coal Limuli. The entire body measures 8 lines in length, and 8 in greatest breadth; of this the head-shield measures 4 lines in length, and 8 in breadth; the anterior (thoracic) part of the post-cephalic shield is 6 lines broad, diminishing to 2 lines near the posterior (abdominal) part; length of the thoracico- abdominal somites 4 lines. The telson measured 4 lines in length. The head-shield is very tumid, the posterior genal angles are not produced ; the glabella is divided down the centre by a slender ridge, its front border (as in most other species) forms two arches, between which and in the front of the head-shield, the larval eye- spots are seen; the small compound eyes are placed midway upon the lateral border of the glabella. The divisions of the thoracico-abdominal segments are only faintly indicated along the central axis of the body ; the margin does not show the usual serrations or spines, as in the other species ; but the number of segments appears to have been the same. The coalesced abdominal segments were marked by a very prominent spine or tubercle, the top of which has however been broken off. I have named this specimen Prestwichia Birtwelli, after its dis- coverer, Mr. Thomas Birtwell, in whose collection the specimens are preserved. W. T. Aveline—Silurian Strata of the Lake District. 441

EXPLANATION OF PLATE X. FIGS. 1 and 2. Hemiaspis limuloides, H. Woodw. Lower Ludlow, Leintwardine. Fig. 1 from the Museum of Practical Geology, Jermyn St.; Fig. 2 from the British Museum. FIG. 3. Fragment of head-shield of Hemiaspis. FIG. 4. Hemiaspis Salweyi, Salter. Lower Ludlow, Ledbury. Coll. Mus. Brit. FIGS. 5 and 7. H. speratus, H. Woodw. Lower Ludlow, Leintwardine. Coll. Mus. Brit. FIG. 6. Hemiaspis horridm, H. Woodw. Wenlock Shale, Dudley. Coll. Mus. Brit. FIG. 8. Bellinurus Kbnigianus, H. Woodw. Coal-Measures, Dudley Coal-iield. Coll. Mus. Brit. FIGS. 9 and 10. Prestwichia Birtwelli, H. Woodw. Coal-Measures, Cornfield Pit, near Padiham, Lancashire. Coll. Mr. Thomas Birtwell.

II.—ON THE CONTINUITY AND BREAKS BETWEEN THE VARIOUS DIVISIONS or THE SILUBIAN STRATA IN THE LAKE DISTEIOT. By W. TALBOT AVELINE, F.G.S., District Surveyor on the Geological Survey of England and Wales. N a former communication1 I stated that the line of division between the Skiddaw Slates and the overlying Volcanic series I(Green Slates and Porphyries), in the neighbourhood of Keswick, was a faulted one, and not an unconformity, as supposed by Mr. Dakyns.2 I added that the evidence of an unconformity (if there was one), between these two series of beds, must be sought for elsewhere than in the district described by Mr. Dakyns. Since then I have examined many miles of boundary between these formations, and have as yet only seen one unfaulted junction, and this is near Bootle, in the Black Combe district, CumbeVland ; but this section at once sets at rest the question of unconformity or conformity. Not only do the Volcanic series lie at the same inclination with the Skiddaw Slates below them, but beds of the latter alternate with beds of the former, showing a perfect sequence and conformity. When the whole of the boundaries between the Skiddaw Slates and Volcanic series are traced, there may be found other spots also showing conformity and passage. The most complete Break in the Lake District is that between the Volcanic series and the overlying Coniston Limestone; and here we have a considerable unconformity. For when the line of division, between these formations from the Granite at Shap to Black Combe is traced, it will be found that the Coniston Limestone series from lying on the highest known beds of the Volcanic series passes suc- cessively to lower and lower beds, till it finally rests on very low beds in the Black Combe district. So great is this unconformity that sometimes the beds of the Volcanic series strike at right angles to that of the beds of the Coniston Limestone. In the Lake District the Coniston Limestone series of beds, which are equivalent to beds on the horizon of the Bala Limestone of North Wales, appear, on a cursory survey, to lie conformably beneath the overlying Upper Silurian rocks ; but undoubtedly this is caused by the local accident of the Coniston Limestone series 1 GEOL. MAG., Vol. VI., p. 382. 2 GEOL. MAO.., Vol. VI., p. 56.