70 



CONCHIFERA. 



Area (Linn.). Ark, Shell solid, somewhat 

 four-sided, marked with strong ribs, often crossed 

 by furrows, commonly covered with a dense fibrous 

 epidermis ; teeth arranged in a straight line, very 

 numerous. 



A. barbata. 



lactea. Fig. 110 ; n. s. 



raridentata. 



tetragona. 



in 



FAMILY II. 



Shell equal-valved, very unequal-sided, the 

 beaks placed far in front, clothed with a dense 

 epidermis ; ligament internal, linear ; hinge tooth- 

 less ; interior surface pearly ; the fore muscular 

 impression small, narrow; the hind one large. 

 Animal attached at will by a byssus ; mantle-edges 

 united between the orifices, which do not form 

 siphons ; foot cylindrical, grooved. 



Modiola (Lamk.). Horse-Mussel. Shell oblong, 

 inflated in front ; beaks blunt ; epidermis often 

 fringed. 



M. modiolus. Fig. Ill ; n. s. M. phaseolina. 

 barbata. tulipa. 



nigra. 



Crenella (Brown). Shell short and swollen, 

 partly smooth, partly marked with radiating lines ; 



