A HISTORY Of VERTEBRATES: FISHES 



441 



Figure 22.12. A group of primitive ray-finned fishes that have survived to the pres- 

 ent day. A, The Nile bichir, Polypterus; B, the shovel-nosed sturgeon, Scaphirhynchus 

 platorhynchus; C, the longnose gar, Lepisosteus oseiis; D, the bowfin, Ainia calva. (A, 

 After Dean; B, C and D, courtesy American Museum of Natural History.) 



reduced to a thin disc. Such a scale is termed cycloid if its surface is 

 smooth, or ctenoid if the exposed part of its surface bears minute 

 processes resembling the teeth of a comb. 



Adaptive Radiation of the Teleosts. The more primitive tele- 

 osts, such as the herring and tarpon (Fig. 22.13 A), are active, predaceous, 



