TYPICAL BIVALVES. 



249 



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

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



Fig. 169. 



Fia. 170. 



Fig. 169.— MytUus edulis, common mussel, with its siphons expanded, and ancliored 

 by its byssiis. — After Morse. 

 Fig. 170. — Cyclocardia ;wya?^g'/^te, nattiral size. — After Morse. 



The foot in the quohog (Fig. 171 A, Venus mercenaria), 

 Mulinia (171 E) and Ciidiophora (Fig. 172) is large, these 



Fig. 171 A. — Venus mercenaria, quohog, natural size, with the foot and siphons. 

 Fig. 171 B.—Maclra {Mulinia) lateralis, natural size.— After VerriU. 



mollusks being very active in their movements. In Glyci- 

 meris (Fig. 173) the fringe is toothless, much as in the 

 oyster. In Mactra (Fig. 174) the middle tooth is large, the 



