54 BIVALVES — ARCA. 



the slopes prominent and angular, giving the shell an 

 eared appearance ; but the anterior slope is far the most 

 prominent. 



The A. concamerata, and A. tortuosa, are the most 

 rare species of this genus. 



The Arcs are found in the European, Indian, Ameri- 

 can, and Atlantic oceans; the Baltic, Northern, and Red 

 seas also produce some species. 



Division l.—With the teeth of the hinge in a straight line. 



Family 1. — Shell twisted. 



Scientific Name. Locality. Common Name. 



Tortuosa Aniboyna, Red Sea Twisted Ark • • • 



Family 2. — Shell rhomboidal. 



Nose E. & W. Indies, Britain . Noah's do-- 



Irabricata . . . .^ . • W. Indies, G.Britain, Me- 

 diterranean, C.G.Hope Imbricated- do •• 



Navicularis St. Domingo Boat do • • 



Plicata Red Sea Plaited do-- 



Candida West Indies, Guinea White • • • • do • • 



Indica Coromandel Indian • • • do • • 



Lactea Britain, Mediterranean • • Milky do • - 



Reticulata West Indies Reticulated do • • 



Family 3. — Shell ohlong or trcmsvenely ovate. 



Magellanica Straits of Magellan Magellanic • do • • 



Lacerata East Indies Hairy do ■ - 



Fusca West Indies, Madagascar Brown • • • • do • • 



Bicolorata Red Sea Party-color'd do 



Modiolus Mediterranean, W. Indies Muscle do • • 



Cor bula Nicobar Isles, C. G. Hope Basket do • • 



Senegalensis Mouth of the Niger Senegal • • • do •- 



