NATURAL SCIENCES OP PHILADELPHIA. 217 



from a sinus in the front margin of the shell ; and I have stated 

 that Pulvinites has a similar mode of growth. Deshayes de- 

 scribes and figures an Eocene Anomia, A. cazenovei, in which the 

 supposed law of retardation is conspicuously indicated by the 

 large size of the shell, although still retaining an incompleted 

 foramen, and now we have this character, probably as a permanent 

 one, associated with the hinge and structure of Ostrea, linking 

 the two genera more closely than was heretofore apparent. 



Ostrenomia has the same affinity to Ostrea that Pulvinites 

 has to Isognomen, Klein. (Perna, Brug.) 



15 



