62 



PALAEONTOLOGY 



Both anterior and posterior laterals are present, one of 

 each in each valve. (In C. plumbea both 30 and the 

 laterals are obsolete i.e., so reduced as to be scarcely 

 recognizable.) As the right anterior-lateral fits under the 



rcsilvum, 



FIG. 17. CRASSATELLA PONDEROSA (LINNE). (x.) 



Right valve above, left valve below. Teeth white, socket? black, 

 (Alter Deshayes.) 



left, while the right posterior fits over the left, the teeth 

 are probably Ai. and An., Pin. and Pn. 



Cvassatella, at the present day, is confined to the 

 Indo-Pacific province and the tropical parts of the 



