BIVALVES. — ARC A. 59 



the margin entire; others, again, are crenulated; and se- 

 veral have prominent angular slopes, which give the shell 

 an auriculated appearance ; the anterior slope is, however, 

 by far the most prominent of the Uvo. 



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. 



ARC A— JrJc. 

 Division I. — With the teeth of the hinge in a straight 



LINE, 



Family 1. — Shell twisted. 

 Tortuosa — Twisted. 



Family 2. — Shell rhoinhoidal. 

 *\i)<E~Noah's. Candida — White. 



*Imbricata — Imbricated. Indica — Indian. 



Navicularis — Boat. *Lactea — Milky. 



Plicata — Plaited. Reticulata — Reticulated. 



Family 3. — Shell oblong or transversehj ovate. 

 Magellanica — Magellanic. Bicolorala — Party-coloured. 



Lacerata — Hairy. jVIodiolus — Muscle. 



h\iscR— Brown. Corhu\a.~Basket. 



Senegalensis — Senegal. 



Family 4. — Shell subcordaie. 

 Laevigata — Smooth. Granosai—Graiiied. 



Pglla Brittle. Rhombea — Rhomboid. 



Antiquata— Antiquated. SemWs— Rugose. 



Family 5. — Gaping. 

 Coniplanata — Compressed. Nivea — White. 



*Bavbata— 5eflr(/erf. C^nce\\a.i^— Cancellated. 



