34 PALAEONTOLOGY OF ILLINOIS. 



7/ , y- 



D. digitatus, N: and W. Sub-carboniferous, Illinois. j Zlri 



[Ctenoptychius digitatus, Leidy.) -TTi , «4*~ v fci 



6. Genus POLYRHIZODUS, McCoy. 



Crown having general structure of Petalodus, but much more 

 elongated, transversely lower, and relatively thicker, as in 

 Chomatodus; root divided into numerous short, robust radicles. 



P. magnus, McCoy, (type). Sub-carboniferous, Gt. Britain. 

 P. porosus, N. and W. Sub-carboniferous, Illinois. 

 P. dentatus, N. and W. Sub-carboniferous, Illinois. 

 P. ponticulus, N. and W. Sub-carboniferous, Illinois. 

 (P. pusillus, McCoy, is a Helodus.) 



7. Genus CHOMATODUS, Ag. 



Teeth transversely much elongated, compressed and de- 

 pressed, crown having the homologous parts of Petalodus and 

 the form and structure of Polyrhizodus ; root short, sometimes 

 obsolete, undivided. 



Ch. linearis, Ag. (type). Sub-carboniferous, Europe. 

 Ch. gracillimus, N. and "W. Sub-carboniferous, Illinois. 

 Ch. cultellus, N. and W. Sub-carboniferous, Illinois. 

 Ch. loriformus, N. and W. Sub-carboniferous, Illinois. 

 Ch. molar is, N. and W. Sub-carboniferous, Illinois. 

 Ch. pusillus, N. and W. Sub-carboniferous, Illinois. 

 Ch. affinis, N. and W. Sub-carboniferous, Illinois. 

 Ch. angidaris, N. and W. Sub-carboniferous, Illinois. 

 Ch. midtiplicatus, N. and W. Sub-carboniferous, Illinois. 

 Ch. elegans, N. and W. Sub-carboniferous, Illinois. 

 Ch. venustus, Leidy. Sub-carboniferous, Illinois. 



