BIVALVES. ARCA. 



51 



There are many Arks which gape at the outer mar- 

 gin ; others, on the contrary, are perfectly close. Some 

 have the margin entire ; others, again, are crenulated ; and 

 several have prominent angular slopes, which give the 

 shell an auriculated appearance j the anterior slope is, 

 however, far the most prominent of the two. 



This genus presents 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 A. nucleus is found fossil, as is also the A. fossilis, 

 in the duchy of Limbourg. 



ARCA.— ^rA:. 



A. — Margin very entire, beaks recurved. 

 Tortuosa — Twisted. 



B. — Margin entire, beak inflected. 



*Noae — Noah^s Ark. Rostrata — Beaked. 



*Barbata — Bearded. SUdata — Striated. 



Modiolus — Muscle. Pulchella — Pretty. 



Pella — Brittle. Afra — African. 



Ovata — Oval. Fossilis — Fossil. 



Pellucida — Pellucid. Cancellata — Cancellated. 

 Minuta — Small. 



C. — Margin crenate, beaks recurved. 



♦Lactea — Milky. Corbicula — Basket. 



Nodulosa — Nodulous. Decussata — Decussated. 



Antlquata — Antiquated. iEquilatera — Equilateral. 



Senilis — Heavy. Fallens — Pale. 



Granosa — Grained. CucuUus — Chambered. 

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