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( 879 ) XXXIII.—Sup}>/Cmentari/ Import on Fossil Fishes Collected Bij The ( 879 ) XXXIII.—Sup}>/cmentari/ Import on Fossil Fishes collected bij the < reo!o</ical Surve}/ of Scotland in the Upper Silurian Hocks of Scotland. By RAMSAY H. THA^UAII:, M.D., LL.R, F.R.S., Keeper of the Natural History Collections in the Roynl Scottish Museum, Edinburgh. (With Three Plates.) (Read July 5, 1901. Given in for publication November 29, 1904. Issu<<l sqiar;it<.-]y January 20, 190f».) Since the publication of my "Report" in December 1899, Mr TAIT, fossil collector to the Geological Survey of Scotland, has been successful in adding a number of specimens of great interest to the valuable series of Scottish Silurian Fishes which supplied the material for that memoir, and with the permission of the Director of the Survey, to whom my best thanks are due, I propose to give descriptions of them in the following Supplement. The search for these remarkable fishes has likewise been taken up by private collectors, and I have therefore pleasure in acknowledging my indebted- ness to Messrs J. YOUNG, of Lesmahagow, P. MACXAIR, of Glasgow, A. WHYTE and F. WHITE, of Muirkirk, and D. NIMMO, of Hamilton, for kindly submitting to me the material resulting from their own work in this field. The present communication is concerned only with the recording of additional facts, further discussion of the theoretical points suggested by the study of these ancient fishes being reserved for another paper. HISTORICAL NOTE. The first finder of these fish-remains in the Silurian rocks of the South of Scotland seems to have been the late Dr SLIMOX, the well-known collector of the fossil Crustacea and Merostomata of the Lesmahagow district. It was from Mr MACXAIR that I received information that the Slimon Collection, now in the possession of Miss SLIMOX, contained examples of Thclodus and Iiirkenia from the "Ludlow" beds of Logan AVater, and I can confirm the fact from personal examination of the specimens. These are, however, imperfect; and as they have no labels, we have no evidence as to whether or not Dr SLIMON recognised them as fish-remains. To Mr MACXAIR I am also indebted for the loan of a microscopic slide of scales of Thelodus Scoticus, apparently from Logan Water, which he found in the collection of fossils formed by the late Dr JOHN YOUNG, and now in the Glasgow Corporation's Museum at Kelvingrove. In this slide the minute structure of the simple dentine substance of which the scales are composed is very clearly shown. In my previous memoir I mentioned the fact that Mr JAMES YOUNG had found a fish in the Logan AVater beds before the locality had been visited by the collectors of TRANS. ROY. SOC. EDIN., VOL. XL. PART IV. (XO. 33). 6 p I!i 880 DR RAMSAY H. TRAQUAIR ON FOSSIL FISHES COLLECTED BY THE the Geological Survey. I have since that time had the pleasure of seeing the specimen, and find it to be a very fair example of Thelodus Scoticus, in which the caudal fin is exceedingly well shown. Order HETEROSTRACI, Lankester. Family CCELOLEPID;E, Pander. Thelodus Scoticus, Traquair. When I wrote my previous memoir, the general configuration of this genus and species was known principally from specimens from the Downtonian beds of Seggholm, Monks Burn, and Birkenhead Burn, those from the Ludlow rocks of Logan Water being more useful for the study of the scales. Since that time, however, specimens have turned up in the last-named horizon and locality which considerably add to our knowledge of the species, and necessitate a correction in the definition of the genus. In Plate I. fig. 4 is represented a specimen of Th. Scoticus collected by Mr TAIT in the Logan Water beds, and showing essentially the same contour as those from the Downtonian horizon, as may be seen by comparing figs. 3 and 4, Plate I. of my former " Report." The fish is in front compressed vertically, and the outline of the lateral flaps is well shown, while behind the tail is twisted so as to display a side view of the caudal fin, of which the upper lobe is unfortunately wanting. The specimen looks indeed short and stumpy compared with some others, but I need scarcely remind the reader that in the absence of an exoskeleton of closely fitted plates, or of a well-ossified endoskeleton, the contour of a fossil fish is extremely liable to variation. Dorsal Jin.—The absence of all fins except the caudal (unless the pectoral flaps are to be looked upon as paired members) was in my former memoir and in my address to the Zoological Section of the British Association at Bradford in 1900 given as a character of the entire family of Coelolepidae, but clear evidence is now forthcoming that, in Thelodus at least, a small dorsal fin was present. It was Mr JAMES YOUNG, of Lesmahagow, who first informed me that specimens of TJielodus Scoticus in his possession had more fins than I had credited the genus with, and to his kindness I am indebted for the privilege of figuring three specimens from Logan Water which show the fin in question. These are represented in Plate I. figs. 1, 2, and 3, the dorsal fin being seen at d. This fin is situated not far in front of the caudal, is small in size, rounded in contour, and covered with minute shagreen scales of the same type as those of the rest of the fish behind the head. I may here mention that, subsequent to my receiving these specimens from Mr YOINC;, Mr TAIT showed me one of the same species from the Downtonian of Seggholm in which the same fin was distinctly visible. Eyes.—In Plate I. figs. 5 and 6 are represented two heads of Thelodus Scoticus, collected by Mr TAIT from the Ludlow beds of Shanks Castle, Logan Water, in which, GEOLOGICAL SUKVKV IN Til 10 UPPER 8ILUKIAN K()(!KS OF SCOTLAND. 881 as already noted in my Bradford " Address," # certain a.ppo;irances are visible which are at least strongly suggestive of eves. These appearances, observed by Mr TAIT himself before the specimens were referred to me, consist of two small dark rounded spots (0), one at eacJi antcro-extenml anole of the licnd, and which come out still more distinctly if the spceimen be wetted with a little water. In %. 5 the dark spots take on a somewhat rin^-shaped appearance, the centre being paler than the circumference. On examination with a strong lens, or with the compound microscope (one inch iJ Of L orrab]T add Ttie i?oo FIG. 1.—Diagrammatic restoration of Thelodus Scoticus, Traq., showing Fin. 2.—A similar outline of Lanarld>/ spinosa, the dorsal fin and the position of the Traq. In this genus (L. horrida) the eyes eyes. The tail is turned round so as have been found, but not the dorsal fin to show the caudal fin in profile. as yet. objective), the spaces occupied by these dark spots are seen to be covered with minute scales like the rest of the skin, but which appear as if stained by a darker colour, VB at which, as already said, is intensified the moment the surface is wetted. As the same phenomenon is also observed in a specimen of Lanarlda horrida, I shall return to it presently in dealing with that genus and species. Scales.—A specimen from Logan Water in the Geological Survey Collection shows beautifully the coelolepid character of the scales, these being split or divided horizon- tally so as to expose the internal pulp cavity. The external sculpture of the pointed * Also in the Summary of Progress of the Geological Surrey of the United Kiiujdnw, for the year 1900, p. 175. 882 DR RAMSAY H. TRAQUAIR ON FOSSIL FISHES COLLECTED BY THE scales of the tail and body behind the head is admirably shown in a specimen lent me by Mr MACNAIR, and from which the drawings of magnified scales given in Plate I. figs. 7 and 8 were taken. Lanarkia horrida, Traquair. A specimen of Lanarkia horrida from Birkenliead Burn (Geological Survey Collec- tion), represented, natural size, in Plate II. fig 1, distinctly displays, even when dry, two small round spots in the same relative position as those in the two examples of Thelodus Scoticus described above, and in like manner, when the fossil is wetted, stand out with all the greater distinctness. On examination with a powerful lens or with the compound microscope (one inch objective), nothing more can be made out than the appearance of a dark bituminous-looking stain at the spots concerned. The white dot seen in the centre of the left dark spot in fig. 1 is due to the carbonate of lime filling up the pulp cavity of a dermal spinelet which has become broken across at this place. That the above-described dark-stained spots represent the position of the eyes in Thelodus and Lanarkia will, I think, scarcely be questioned, and indeed the pheno- menon does not stand alone in the field of fossil ichthyology. In the case of the little Cyprinodont fish Prolebias cephalotes (Ag.), which occurs in shoals in the Lower Oligocene of Aix in France, the pigment of the eye, as well as of the abdominal cavity, is preserved; and on a slab of fissile grey shale from China, and probably of Jurassic age, now before me, numerous specimens of a small Lycoptera show a conspicuous round black spot occupying the well-defined interior of the orbit. That no definite orbits are observable in the case of the Coelolepidse is inseparable from the non-coherent nature of the elements of the exoskeleton.
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