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. 
Drviston 1.— With the teeth of the hinge ina straight line. 
Famity 1.—Shell twisted. 
Scientific Name. Locality. Common Name. 
Tortuosa -------- Amboyna, Red Sea ----- Twisted Ark --- 
Famity 2.—Shell rhomboidal. 
Nowe>-++++----- E. & W. Indies, Britain. Noah's --<- do - 
Imbricata-.....» W.Indies, G. Britain, Me- 
diterranean, C.G. Hope Imbricated- do -- 
Navicularis->---- St. Domingo-+---.-++++- Boat --+-++ do «+ 
IPNiGataiocicaeicic eters REGS Gave ictsrcietetereteidt-lsheieiai- Plaited ---- do -- 
Candida ---.-.-- West Indies, Guinea-:--- White ---- do-- 
ANGIGal eters es dere Coromandel---.--.-.++.. Indian --- do-- 
Lactea+++++ee.6- Britain, Mediterranean -- Milky ---- do -- 
Reticulata------- West Indies -.--.2-++-:- Reticulated do -- 
Faminy 3.—Shell oblong or transversely ovate. 
Magellanica ----- Straits of Magellan ----- Magellanic: do -- 
Lacerata --ce+-s. Biastalindt@s) yam cisco) solace Hairy vie ware do «- 
Fusca +++--+++-» West Indies, Madagascar Brown -+-- do -« 
Bicolorata------- Red Sea-eeeeeeeeeeecees Party-color'd do 
Modiolus------+- Mediterranean, W. Indies Muscle---- do -- 
Corbula----+-+-- Nicobar Isles,C.G. Hope Basket ---- do -- 
Senegalensis - ---- Mouth of the Niger----- Senegal --» do -- 
