232 PALEONTOLOGY OF ILLINOIS. 



longitudinal rugae, and showing beneath the vertical prismatic struc- 

 ture and punctse, the latter minutely and closely pitting the worn 

 areas in front ; the crown also shows the broadly arched lines of 

 growth to which the posterior margin in worn individuals more or 

 less conforms. The basal portion of the tooth is not known. 

 Transverse diameter of tooth across the posterior margin at least 

 9 mm; length along median line 7.5 mm. 



The above described species is represented by a unique example 

 discovered by Dr. George Hambach, showing nearly the entire coro- 

 nal area, but the basal portion is destroyed, and the posterior 

 margin worn even with the broadly arched curvature of the lines of 

 growth. The postero-lateral cornua are also absent from the same 

 cause; otherwise the specimen clearly displays its distinctive 

 peculiarities. Compared with the preceding species from the St. 

 Louis limestone, Copodus Van Hornii, the present form is dis- 

 tinguished by its more angular outline, the lateral borders much 

 less rapidly converging anteriorly, and perhaps the more uniform 

 convexity of the coronal surface. The specimen somewhat resem- 

 bles certain forms from the Irish Lower Carboniferous deposits 

 referred by Professor Agassiz to the intimately allied genus Pinnnc- 

 odus : but if we correctly interpret the distinctive peculiarities of the 

 latter genus, the present tooth differs in not possessing the emar- 

 ginated anterior margin which characterizes that genus, as 

 represented by the typical form P. gonoplax, Agass. 



Geological position and locality : Chester limestone ; Chester, 111. 



