GANOIDEI. 



353 



steus, but with a simple arched dorsal shield. As ia this 

 latter genus the caudal extremity does not possess external 

 or internal bony parts, and the ventral plastron of both 

 genera corresponds in every particular; the dentition is so 



Fig. 136. — Ventral aspect of Pterichthys, after Pander. 15, mandible (?) ; 

 16-21, ventral tucklers. 



singularly Like that of Lepidosiren, that Newberry (Geolog. 

 Survey of Ohio, vol. ii. part 2) considers this genus to be in 

 genetic relation to the Dipnoi. The following genera have 

 been united in a separate family, Cephalaspidce ; viz. Cephal- 



2a 



