FOSSIL FISHES. 49 



Smaller form without lateral denticles, from 2 to 3 lines high, central 

 cone and base as in larger form. These small teeth occur in large num- 

 bers in tlie fish bed discovered by Mr. Jay Terrell in the valley of Black 

 River. As will be seen from the description given above, they differ 

 much among themselves in form and size, but between the extremes are 

 all possible shades of variation. The peculiar yoke-shaped and cupped 

 base is the same in all, but some have no lateral denticles, others have 

 tubercles at the sides of the central cone, while others still have two well- 

 developed lateral cones. This diversity is not greater than we find in 

 the dentition of modern sharks, and it is highly probable that in all of 

 the species of Cladodus, the teeth were more or less variable in size 

 and form according to the places they held in the mouth. This intro 

 duces an element of uncertainty in the diagnosis of species from a few 

 teeth, which should be kept in mind in describing or discussing species 

 of this and other genera of extinct sharks. It is not probable, however, 

 that the species of Cladodus have been very much multiplied from this 

 cause, for the reasons that : (1) the number of species yet described is 

 small, (2) they are distributed through a great vertical and geographical 

 range — ^from the base of the Devonian to the Permian, and from Russia 

 to Kansas — ^very few having bee^p taken from the same stratum and 

 locality, and (3) the dentition of each species, however much varied, has 

 generally something in common, of form or ornamentation, by which the 

 different members of the series may, with due care, be identified. 



The danger of multiplying species from this cause is at least not suffi- 

 cient to make it necessary or wise to neglect all material of this kind 

 until such time as the complete dentition of each species shall be discov- 

 ered. This cannot be hoped for in regard to many fossil sharks, as their 

 skeletons were cartilaginous, and the connection between the teeth and 

 jaws was ligamentous and was dissolved in decay. In the only cases that 

 have come under my observation where any considerable portion of the 

 dental series has been found with the teeth in position {Cladodus Patter- 

 soni and Diplodus oompressus), the only difference visible among sorae 

 hundreds of teeth shown is in size. Had the entire dentition of both 

 jaws been visible in these cases, their testimony would have been more 

 conclusive, but it has much weight as it is. 



Cladodus Komingeei (n. sp.). 



Teeth small, breadth of base 7 lines, height of median cone 5 lines ; 

 central cone flattened behind, anterior face rounded ; basal portion of 

 posterior face deeply sinused ; lateral cones two pairs (sometimes with a . 



