CONCHIFERA OR BIVALVES. 75 



thick; their locality is New Holland and the 

 southern seas. 



28. Mesodesma (Deshayes). — Shell ovate, 

 transverse or triangular, equivalve, rather com- 

 pressed, and generally closed; the hinge has two 

 thick lateral teeth in each valve, between 



which is situated a deep spoon-shaped cavity 

 for the ligament. Animal, foot very flat, qua- 

 drangular. — 10 species. 



29. Erycina. — Shell transverse, small, and 

 resembling the Cras- 

 satella, but having ob- 

 long lateral teeth, and 

 rarely gaping ; liga- 

 ment small, placed in 

 a triangular pit. Ani- 

 mal unknown. — 2 

 species recent, and 10 fossil. 



