56 MOLL USC A. 



Mussels (Mytilida). The black mussels with tneii 

 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, M). By means of their 

 foot, /", they fasten a silken cord to the rocks, then another, 

 and by continually stretching out cables ahead or upward. 



FIG. 58. Group of headless mollusks. c, cardium springing ; M, mytilus ; 

 s, pecten ; R, razor-fish, solen ; /", foot ; /, anchoring-threads ; si. 

 breathing-siphons ; , eyes of scallop. 



and lifting and breaking off those below, they climb 01 

 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 ( Unionidce). These are 

 pond, river, and lake mussels, resembling in appearance 

 the edible mussel, black without 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 



