AVICULAD^. 71 



hinge-margin notched behind the ligament ; interior 

 brilliantly pearly. Animal crawls freely about 

 sea-weeds by means of its long foot. 



C. costulata. C. faba. 



discors. Fig. 112 ; n. s. marmorata. 



decussata. rhombea. 



discrepans. 



Mytilus (Linn.). Mussel. Shell wedge-shaped, 

 round behind, the beaks forming a sharp point in 

 front. 



M. edulis. Fig. 113; ^n.s. 



113 



Family III. Aviculad^. 



Shell unequal- valved, very unequal-sided ; the 

 beaks near the front ; epidermis wanting, or indis- 

 tinct ; interior generally pearly ; hind muscular 

 impression large, nearly central ; fore one small, 

 within the beak ; pallial line reduced to a series of 

 dots ; hinge line straight, lengthened, wholly or 

 nearly toothless. Animal with the mantle not 

 adhering to the valves, entirely open, prolonged 

 into irregular lobes without siphons, the edges 

 fringed ; foot small, grooved, spinning a strong 

 byssus. 



