492 Dr. E. H. Traquair on the 



on the outer aspect, and two are similarly placed on the inner 

 aspect of the limb. 



The Tail. — In most Scottish examples of Pterichthys more 

 or less perfect remains occur of a tail, covered with small 

 rounded or somewhat hexagonal, slightly imbricating scales, 

 which are arranged in longitudinal rows and also in transverse 

 bands, the scaks of one band alternating with those of the 

 next ; on the dorsal aspect close behind the carapace is also 

 a small fin (PI. XVII. fig. 3). Along the dorsal margin the 

 scales are different in shape trom those on the sides ; in front 

 ot the fin they seem to be in the form of a few narrow, lon- 

 gitudinal, median plates ; behind it tliey are elongated and 

 imbricating, the arrangement reminding us of the so-called 

 fulcra or V-scales along the extremity of the tail of an Acipen- 

 seroid fish ; but whether they are monostichous or disti- 

 chous it is hard to determine. The external sculpture of the 

 scales is rarely seen, and can therefore hardly be available as 

 a specific character. (See Agassiz's figure of the scales of 

 It. cornutus in 4, pi. ii. fig. 3.) 



'Lh.ejin is triangular-acuminate in shape and seems to have 

 been covered with small scales, no distinct rays being seen. 

 At least two specially prominent elongated scales are placed 

 along its anterior margin, producing an appearance which 

 has been mistaken for that of a spine. Tlie position of this 

 fin is undoubtedly dorsal, as held by Hugh Miller, and not 

 anal, as supposed by M'Coy (6, p. 59D). iSir Philip Egerton 

 supposed that in addition to the dorsal two ventrals were also 

 present (9 a, p. 127) ; but having examined the specimen, now 

 m the British Museum, on which he founded this conclusion, 

 1 find that the two supposed ventrals are merely parts of the 

 dorsal separated by a little fault or dislocation in the stone. 



As regards the British species of Pterichthys I have already 

 indicated my views in the ' Geological Magazine ' of last 

 month. Their characters, so far as I can see, are entirely 

 dependent on slight differences in tne shape of the carapace 

 and of the terminal segment of the arm, so that I have often 

 suspected that after all only one " good " species was really 

 represented. Were this view to be adopted, then the name 

 ittrichtltys Milltri, Ag., would include all the others as 

 varieties. 



ASTEEOLEPis, Eichwald (published April 1840). 



{= Asterolepis, Agassiz, pars, non Hugh Miller; Fterichtki/s, Owen, 

 W iiiteaves, et cet. aiict. pars, noii Agassiz.) 



We have seen that Pander maintained the identity of 



