50 BIVALVES. ARCA. 



smooth or muricate grooves, not unfrequently having 

 their whole surface covered with a brownish or greenish- 

 black epidermis. 



The next form that the ark presents itself in, is that of 

 a roundish or suborbicular description. The Area Gly- 

 cymeris and pilosa are sufficient examples; they are for 

 the most part smooth on the outside, except where the 

 longitudinal striae are placed ; which striae are frequently 

 more articulate in the interior than on the exterior, and 

 often terminate at the inner margin, in determined ele- 

 vated teeth. 



This genus contains but little beauty, though some of 

 its species are considered rare. 



The Ark is found in the European, Indian, American, 

 and Atlantic oceans : the Baltic, Northern, and Red sea» 

 also produce some species. 



Th e Area nucleus is found fossil, as is also the Area 

 fossilis, in the Duchy of Limbourg. 



ARCA. 



A. Margin very entire^ beaks recurved. 

 Tortuosa. 



