TYPICAL BIVALVES. 



249 



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

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



FIG. 170. 



Fig. 169. Mytilus edulis, common mussel, with its fringe expanded, and anchored 

 by its bysBiis. After Morse. 

 Fig. VtQ. Cyclocardia novangliib, natural size. After Morse. 



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

 Mulinia (171 B) and Clidiophora (Fig. 172) is large, these 



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

 Fig. 171 B.Mactra (Mulinia) lateralis, natural size. After Verrill. 



mollusks being very active in their movements. In Glyri- 

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

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



