852 DR RAMSAY H. TRAQUAIR ON FOSSIL FISHES COLLECTED BY THE 



occurs in the former. The position of the orbits in Pteraspis on the edges of the 

 anterior part of the carapace is relatively identical with that of the rounded depressions 

 which I take to represent orbits in Drepanaspis. But there is no distinct specialised 

 rostral plate in Drep>anaspis, and the mass of small polygonal ones which surround the 

 median plate have altogether disappeared in the Pteraspidse. 



Then again on the under surface of Drepanaspis there is a great median ventral 

 plate, comparable to that of Pteraspis, though it is again surrounded by small ones like 

 the dorsal one above. 



So far as the arrangement of the plates of the carapace is concerned, Pteraspis then 

 suggests to us a specialised form of Drepanaspis. 



The tail of Pteraspis is only known by three fragments, two of which, were figured 

 by Lankester (xiv., PL V., figs. 1, 3, 5, 8). One of these, from Cradley, Herefordshire 

 (tab. cit., figs. 3 and 8), and now in the British Museum, is the basis of the restored 

 squamous portion of the tail in Lankester and Smith Woodward's reconstructions, and 

 shows that this part was covered by somewhat imbricating rhombic scales. The second 

 specimen, from the Powrie collection, and now in the Edinburgh Museum of Science 

 and Art, is from the Bridge of Allan, where it occurred along with carapaces of 

 Pteraspis Mitchelli, Powrie. To „tbis specimen Lankester did not devote much 

 space in his monograph, merely remarking (op. cit., p. 33), under Pteraspis Mitchell I, 

 that " a few rhomboidal scales also obtained by Mr Powrie from this locality (PL V., 

 fig. 1) probably belong to this or another species." 



This patch of scales is, however, worthy of careful examination. As may be seen 

 in Prof. Lankester's figure, it is a narrow band two inches in length by three-eighths 

 in breadth, starting apparently from a larger mass, of which the remains are, however, 

 no more than barely indicated. It is to be noted that the scales, quadrangular in form, 

 become smaller towards what was apparently the distal extremity of the patch, while 

 on one aspect there is something to be seen which Prof. Lankester had apparently 

 overlooked— namely, some undoubted remains or traces of a fin-membrane covered by 

 minute scales. I have therefore no doubt that this specimen is the remains of the 

 upper lobe of a heterocercal Pteraspidian tail, and belonging in all probability to 

 PL Mitchelli. 



The tliird example is from the Lower Devonian of the Khine country, and has been 

 briefly alluded to by Prof. Schluter (xxx. p. 125) under the name of Scaphaspis 

 Bonnensis. The specimen is in the Geological Museum of the University of Bonn, 

 where I have on two occasions had the opportunity of looking at it for a few moments, 

 but I did not find that it showed anything more than the fact already known — 

 namely, that the Pteraspidian tail was provided with a covering of small scales. 



The tail, then, of Pteraspis, so far as we know it, is also in accordance with that of 

 Drepanaspis, and the conclusion seems to me to be certainly warranted — namely, that 

 the Pteraspidse are related to the Drepanaspidse as more highly specialised forms of 

 one common series. 



