146 



TRANSACTIONS OF THE AMERICAN PHILOSOPHICAL SOCIETY 



thoroughly investigated by Ridewood (1904a, b), show an extraordinary diversity in general 

 habitus joined with a fundamental identity in family heritage. The typical plankton- 

 feeding genus Clupea (Fig. 38) has very delicate teeth with jaws of moderate length; the 



temporal 

 foramen 



V 



\ 



preppictic 

 fossa. 



pf&parpth , 



'proot 



hyom 

 temp fen /', pto 



sphot 



^ Clupea finta 



C. harengas 



Fig. 38. Clupea finta. After Ridewood. A. Neurocranium. B. Syncranium. 



general form of the skull also is normal in appearance. The large maxilla forms the side 

 of the gape. In the predaceous Chirocentrus (Fig. 34) (whose skull characters ally it with 

 this family) the strong upturned mandible supports a few very large recurved teeth; in the 

 toothless Chato'essus (Fig. 39) the head is very short and dorso-ventrally deep, the gape 



