VARIOUS SPECIES OF CTENODUS. 57 



be considered of generic importance. They point out, neverthe- 

 less, the propriety of retaining for the present, at least, until 

 more is known respecting them, the generic appellation of Cte- 

 nodus for our Coal-Measure Ctenododipterini. 



The body of the Nevs^sham specimen is not well defined ; but 

 as far as the general characters can be determined, they agree 

 with those of Dipterus. The head is apparenly round and short, 

 being about one-fourth the length of the entire fish, which is 

 three inches long ; and it exhibits in a distinct manner the un- 

 der side of the basisphenoid and the praesphenoid bones united 

 together. They assume the form of a rhomboidal plate, with 

 a flattened process extending from the anterior and posterior 

 angles; the bones bearing the dental plates have been displaced. 

 The two opercula, which are each formed of a single piece, are 

 equally distinct ; they are thick and well-rounded, being only 

 slightly elongated transversely, and have the upper or hinge- 

 margin flattened, the surface irregularly granulated, punctured, 

 and enamelled. The tail is in a confused state ; but there can 

 be little doubt that it is heterocercal, of the rhomboidal type. 

 And there are traces of an anal and a ventral fin immediately 

 before the caudal ; but it is impossible to say whether or not they 

 are lobed. There are a few slender curved bones scattered about 

 behind the head, which have the appearance of ribs ; these, and 

 the bones of the head alone have been ossified ; the vertebras 

 have all disappeared. 



Such is the description of the C. elegans, so far as it can be 

 determined by the imperfect remains of the specimen in our pos- 

 session. That it is specifically distinct from the Old Eed Sand- 

 stone species is evident enough; and it seems quite probable 

 that it even differs from them generically. It is much smaller 

 than most of the Dijjteri, though it is apparently not full-grown, 

 as the teeth are considerably smaller than the largest specimens 

 of them belonging to this species in our possession ; and, on ac- 

 count of its minuteness when compared with the largest species 

 of Ctenodus from the Coal-Measures, there is some doubt whe- 

 ther it may not bo generically different also from them. It is not 

 more than three inches long, as has been alrcad}' stated, while 



