34 



BIVALVES. 



ARCA. 



grooves, not unfrequently having their whole surface co- 

 vered 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 tlie 

 longitudinal stri£e are placed; which striae are frequently 

 more articulate in the interior than on the exterior, and 

 often terminate at the inner margin, in deterimned 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 seas, 

 also produce some species. 



The Area Nucleus is found fossil, as is also the Area 

 Fossilis, in the Duchy of Limbourg* 



ARCA. 



