56 MOLLUSCA. 
Mussels (A/ytilidz).—The black mussels with their 
silvery interiors are the common forms on the rocks of the 
Eastern Shore. They are covered with a thick leathery 
skin, the hinge being without teeth. They are remarkable 
for their climbing powers (Fig. 58, 47). By means of their 
foot, f, they fasten a silken cord to the rocks, then another, 
and by continually stretching out cables ahead or upward. 
Fic. 58.—Group of headless mollusks. c, cardium springing; J/, mytilus; 
s, pecten; &, razor-fish, solen; /, foot; 7, anchoring-threads; sé, 
breathing-siphons ; e, eyes of scallop. 
and lifting and breaking off those below, they climb or 
warp themselves along very much as does a ship on a lee- 
shore ; 217 living and 350 fossil species are known. 
VALUE.—The edible-mussel fisheries afford employment to many 
persons in Europe. 
Fresh-Water Mussels (Uxionide).— These are 
pond, river, and lake mussels, resembling in appearance 
the edible mussel, black withuut and pearly within, tinted 
with iridescent hues. About 550 living species are known 
throughout the world, and 60 fossil. The sexes are dis- 
tinct. The young are held in the gills of the mother in 
