GENERA PRODUCTUS AND STROPHALOSIA. 



149 



I have moreover ascertained that the American forms of P. cosfatus 

 have often a well defined area on the ventral valve, and a narrow area 

 on the dorsal valve, extending nearly the entire length of the hinge-line ; 

 and in some specimens, this is as distinct as the area of Strophodonta or 

 of Chonetes. There is of course a foramen, which is open in the examples 

 observed ; though in Mr. Davidson's figure of P. semireticulatus, cited 

 above, the foramen is closed by a deltidium. The specimens of ventral 

 valves of Productus, which I have been able to examine, have no true 

 teeth or extensions from the margins of the foramen ; but sometimes a 

 callosity extends obliquely backward and unites with the interior of the> 

 shell, being in fact as much a representation of dental lamella3 as we 

 have in some species of Strophodonta.* The accompanying figure 8 illus- 

 trates the hinge-area of P. costatus ; and figure 7 is of the interior of a 

 dorsal valve, showing the muscular and vascular impressions. 

 7 8 



Fia. 7. PaoDUCTUs costatcs. 



Interior of the dorsal valve to show the reniform 

 vascular improssions, cardinal process and the 

 oblique callosity C. 



Fio. 8. Peoductds costaics. 



Dorsal view of a specimen showing 

 the hinge-area. 



Thus we see that the species referred to Productus may have all the 

 characters of Stropiialosia except the hinge-teeth and sockets, and the 

 disposition of the reniform impressions ; while the New- York species, 

 possessing teeth and sockets, have not the disposition of the reniform 

 vascular impressions which are given by European authors as characte- 

 ristic of Strophalosia. 



In glancing at the species of Productidae illustrated on Plates 23, 24, 



• See Strophodonta demissa, S, reversa, S. nacrea and others. 



