DR RAMSAY H. TRAQUAIR ON THELODUS PAGEI. 601 



angulated instead of being regularly curved. In this specimen it is also to be noted 

 that where the scales are broken horizontally the internal cavity is reduced to a 

 mere narrow cleft as seen in fig. 7. 



The extreme softness of the scales in both of these specimens renders it impossible 

 to extract or isolate any one of them as they crumble away at once if any attempt 

 is made to develop them with a needle or other sharp instrument ; nevertheless, the 

 examples which I have figured just as they lie in the stone afford us a very good idea of 

 their configuration. Their friable condition is also adverse to their being examined 

 microscopically. Seen with a powerful platyscopic hand lens, the substance of the scales, 

 where broken across, is white pearly and homogeneous in texture, some traces of con- 

 centric lines being occasionally observable as in the fractured example shown in fig. 4. 



A consideration, however, of the macroscopic character of these dermal appendages 

 leaves no doubt that the fish before us belongs to the family Ccelolepidse of Pander, 

 and that it throws a startling light upon the bodily configuration of fishes, of which, 

 as aforesaid, we have hitherto known nothing but the detached scales. This is 

 clearly shown by the general form of the scales, by the internal pulp cavity, as well 

 as by the opening in the lower surface of the base, which in those of the entire 

 specimen is pretty large (fig. 3), while in those of the shagreen-fragment it is very 

 small as in fig. 8, or even apparently absent as in figs. 5 and 6. 



There is also as little doubt that the genus Thelodus itself (Thelolepis, Pander, 

 Rohon) is the one to which this species from the Forfarshire Old Red is referable. 

 Rohon's suppression of Nostolepis, Pander, is here clearly justified by the scales of 

 the shagreen-fragment to which I have just alluded, in many of which no basal 

 opening can be seen, while in others it is present. And if I am right in referring 

 this fragment to the same species as the entire fish represented in fig. 1, then a 

 question comes up as to the validity of the genus Ccelolepis. 



For the essential difference between Ccelolepis and Thelodus is the larger size of 

 the pulp cavity and basal opening with a feebler development of the base in the 

 former, while in the latter the case is reversed. To quote Rohon's words : — 



" Placoidschuppen mit weiter Pulpahohle mid rudimentarer Basalplatte . . Ccelolepis. 

 Placoidschuppen mit kleiner oder rudimentarer Pulpahohle und wohl 



entwickelter Basalplatte Thelolepis." 



It is to be observed, however, that in the scales of the entire and presumably 

 younger specimen of Th. Pagei (figs. 1-4) the pulp cavity and basal opening are 

 proportionally larger than in the scale of the shagreen-fragment (figs. 5-8) which 

 evidently belonged to an older and larger fish. Here the pulp cavity and basal open- 

 ing have been evidently reduced by the progress of calcification advancing with 

 age ; and it may well be asked — may not the supposed distinction between Ccelolepis 

 aud Thelodus be entirely of this nature ? I, for my part, am inclined to reply in 

 the affirmative. 



