GNATHODON. 



Muscular impressions two, lateral; muscular impression 

 of the mantle with a small sinus ; ligament internal, in a 

 deep pit, proceeding from the umbo. 



Distinguished from Cyrena, which it most nearly 

 resembles, by its having an internal ligament, and from 

 Crassatella, by its olivaceous epidermis, and its eroded 

 umbones. Gnathodon appears to us to connect the family 

 of the Mactracece with the genera Cyrena and Cyclas. In 

 its teeth it differs materially from all others, they have, 

 however, one circumstance in common with several Cy- 

 renae and with some Mactraceae, namely, that of the 

 lateral elongated teeth being crenated. All the specimens 

 we have seen are beautifully white within. 



Our plate represents Gnathodon aineatus. 



