EXTINCT ALLIES OF THE STURGEON. 



73 



The Platysomatidse (198) are extinct fishes ranging from the 

 Carboniferous to the Permian. The body is laterally compressed 

 and rather deep in a vertical direction, with a close investment of 

 rhombic scales ; the base of the dorsal fin is extended, the tail 



heterocercal. As in the previous family there are broad branchio- . 



stegal rays, with an anterior median plate in front. The jaws are dus. 

 short and stout, the teeth obtuse. The principal genera are 

 Cheirodus (198, and fig. 43), Eurynotus, and Platysomus. 



