VERTERRATES. 363 



PELTODUS UNGUIFORMIS, N. and W. 



PL ii, fig. 7, 7o. 



> 



TEETH small, ovoid in outline, thin, convex above, concave 

 below ; antero-posterior diameter of largest individuals half 

 inch ; lateral diameter quarter inch ; anterior margin broadly 

 rounded, posterior portion narrowed to the abruptly rounded 

 or truncated edge ; crown surface obscurely punctate over 

 the middle and posterior parts, distinctly so on anterior slope 

 which formed the triturating surface. 



There are several of these little teeth in the collection, all from the upper 

 Coal Measures, and all alike in the generalities of form and structure, though 

 varying considerably in size. They are quite thin and are the smallest and 

 most delicate of all the great series of crushing teeth which have been obtained 

 from the Carboniferous strata of Illinois. In general aspect they are not un- 

 like a small, much-curved nail of the human hand ; a resemblance which has 

 suggested the name given to the species. 



Formation and locality : Upper Coal Measures ; La Salle, III. 







GENUS CYMATODUS, N. and W. 



TEETH of medium or small size, oblong or elliptical in out- 

 line, thin, forming a flat or arched plate of which the crown 

 surface is transversely undulated and uniformly punctate ; 

 under surface flat and smooth, at the posterior end bearing a 

 narrow, strap-shaped, oblique root. 



This genus is created to receive a quite perfect and peculiar tooth from the 

 Coal Measures, of which a more detailed description is given below. This 

 tooth has much in common with Deltodus and Pcecilodus, and was doubtless used 

 for precisely the same purposes in the same manner. It has, however, no defin- 

 ite deltoid form, and no ridges or furrows which follow the line of curvature, 

 as in Deltodus, nor yet the banded structure of crown surface which is the most 

 prominent character of Pcecilodus ; and more than in all things else it differs 

 from the teeth of the genera cited, by its long, narrow, back-reaching root. 



No teeth bearing any close resemblance to this have been found in the 

 Lower Garb, limestone, and it probably represents a genus of Plagiostomous 



