as a guide to distinguish them from the G. Venus, that 

 they all have four primary teeth on one valve, and ou- 

 ly three united on the other, with an isolated cavity, 

 oval, and parallel to the margin, the lateral teeth di- 

 vergent to the summit. 



They are all marine shells, solid, regular, equivalve, 

 inequilateral, apices equal, recurved and slightly pro- 

 jecting. Four primary teeth on one valve, and three 

 on the other, with a distant cavity parallel to the edge, 

 not at all connected with those which receive the car- 

 dinal teeth, they being placed in a different direction. 



Internal Margin of the Valves very entire. 



Anterior cardinal Toothy with a striated canal, or its 

 Sides uneven. 



Cytheria lusoria Cytheria graphica 

 petechialis morphina 



impudica purpurata 



castanea casta 



zonaria corbicula 



meretrix tripla. 



