TYPICAL B1VAL7ES. 



229 



grooved, with a gland for secreting a bundle of threads, the 

 lyssus, by means of which it is anchored to the bottom. 



Fig. 163. 



Fig. 164. 



Fig. 163. — Mytilus edulis. common mussel, with its fringe expanded, and an- 

 chored by its byssus. — After Morse. 

 Fig. 164. — Cyclocardia novangliae^ natural size. — After Morse. 



The foot in the quohog (Fig. 165 A, Venus mercenaria), 

 MuUnia (166 B) and Glidiopliora (Pig. 167) is large, these 



Fig. 165.4. — Venus mercenaria, quobog, natural size, with the foot and siphons. 

 Fig li6B,—Mactra (MuUnia) lateralis, natural size.— After Verrill. 



mollusks being rery active in their movements. In Glyci- 

 meris (Fig. 168) the fringe is toothless, much as in the 

 oyster. lii Mactra (Fig. 169) the middle tooth is large, the 



