28 FISH OF THE CARBONIFEROUS PERIOD. 



thirteen or fourteen very strong, single or dichotomous ridges, 

 the sides of which are usually cut by numerous deep oblique 

 sulci ; the ridges are highest at the base, where they terminate 

 abruptly ; osseous base a little wider than the crown. Diameter 

 of base 3 to 4 lines. 



This tooth presents considerable variation in the proportion of 

 height to width of the base, and also in the number and rela- 

 tive thickness and complexity of the ridges ; there is no variety 

 however sufficiently striking to require particular notice or occa- 

 sion any difficulty in the identification of the species. 



It seems abundant in some parts of the Derbyshire limestone. 



{Col. Cambridge University.) 



Hybodontes. 



Cladodus Icevis (M^Coy). 



Sp. Char. Principal cone very thick, slightly oblique, its height 

 equal to half the width of the root ; secondary cones two on 

 each side, very strong, the outer largest and divaricating, 

 nearly half the length of the principal cone ; all the cones ob- 

 tusely rounded at the summit, very slightly tapering, and the 

 height of each slightly exceeding the width of its own base ; 

 base of the crown and osseous root concave ; surface of all the 

 cones smoothj highly polished. Width of crown 9 lines, height 

 of principal cone from the basal margin 5 lines. 

 This closely resembles the C. marginatus (Ag.) in size and 

 form, but the cones taper less and the species is fully distin- 

 guished by its smooth surface, destitute of the coarse longitudinal 

 plaits or striae of that or the allied species. 

 Carboniferous limestone of Armagh. 

 {Col. University of Cambridge.) 



