Notes on Carboniferous Selachii, 417 



location among the Chiinaeroids, as maintained by Professor 

 Hasse.^ That it is a Hybodont cannot, in my opinion, be 

 doubted. 



Orodontid^, De Koninck. 



If the mesozoic genus Acrodus is a Hybodont, and its 

 spines are generically indistinguishable from those of 

 HyhoduSy it is difficult to draw any line between the 

 Hybodontidse and Orodontid?e. 



One of the genera which De Koninck and Mr Davis 

 place in this family must, however, go — namely, Lophodus 

 of Eomanowski. Eomanowski separated from Agassiz's 

 Helodus such forms as didymus, Icevissimus, mammilla^Hs, as 

 havin.oj one or more prominent elevations on the crown, and a 

 well-developed, compressed and vertically striated root ; while 

 he considered H. planus, which has no such root and no 

 special elevation on its crown, to represent the old genus. 

 Unfortunately both " Helodus " planus and " Lophodus " didy- 

 mics belong to the mouth of the same fish, and that fish is 

 Fsephodus magnus ! Moreover, as I have once remarked, if 

 the old genus Helodus were to be divided, surely the cha- 

 racters of the type species H simplex of the Coal-measures 

 ought first to be ascertained and duly considered. Now, a 

 fine series of specimens of Helodus simplex, Ag., in the col- 

 lection of Mr John Ward, F.G.S., Longton, clearly shows that 

 the teeth in this species have the form of "Lophodus ;" that 

 the entire dentition consisted of teeth generally similar in 

 shape ; and that the dorsal fins were armed with spines re- 

 sembling those of Pleurodus. Whatever be the nature of the 

 teeth which Mr J. W. Davis retains in and adds to Helodus, 

 there can be no doubt that H. simplex must remain the type 

 of Agassiz's genus, and in which also Chomatodus ductus, Ag., 

 ought to be placed, as already indicated both by M'Coy and 

 Davis. 



COCHLIODONTID^. 



The closeness of the alliance between the Cochliodontidte 

 and Orodontidse is shown by the fact that the anterior teeth 



1 NatiirlicTies System der ElasmobrancMer. 



