CONCHIFERA OR BIVALVES. 



97 



57. Nucula. — Shell varying in shape, 

 equivalve, inequilateral ; teeth 

 small, numerous, and prominent, 

 with a large spoon-shaped one in 

 the middle; hinge curved or 

 straight; bosses contiguous and 

 curved; ligament partly inter- 

 nal; epidermis green, or dark olive brown. 

 Animal, foot large but thin. — 10 species recent, 

 7 fossil. 



The localities of this genus are the Baltic 

 and Mediterranean, the Indian Seas, the En- 

 glish Channel, &c, where they are met with on 

 the sand and mud, either on the open coast or 

 at the mouth of rivers. The shell is generally 

 pearly inside. 



58. Trigonia. — Shell pearly; cardinal teeth 



H 



