192 SPECIFIC DESCRIPTION. 



as the valves are constructed so as to lie partially 

 one over the other, and from the muscular con- 

 traction of the animal are doubtless often so ar- 

 ranged. But it can hardly be denominated Cryp- 

 toconchus, as a considerable part of the shell is 

 not hidden. The two species porosits and larvce- 

 formis are however obviously of the same genus. 



