Tin: SNAILS 



71 



which it ie anchored to the bottom. The fool in the quo- 

 hog (Fig. 78, I. Venus mercenaria; 78, B, Mulinia) is 

 large. 



The Bhip-worm ( Fig. ','.>) belongs to this class. The body 

 is Blender ami worm-like. The shell is minute, tin- soft 

 animal 1 i \ i 1 1 _r in a burrow lined with linn This ani- 



mal develops like other tnollusks; the young (] - . B) 

 having two equal shells in-- •!< «si mr the body, ami swimming 

 by its ciliated velum or sail (r). After the foot ( Fig. 8< . 

 is well developed i • the piles of wharves and lloating 



c 



Fio. 80.— ]' ent of the Ship- worm. 4, epg, with the yolkoncedh 



£, theveliger enclosed by the bivalve shells; C, ad rwiththe 



large fuut \f) and velum 



wood, into which il bores and completes its metamorph 

 On the ooasl of New England the ship-worm lays 

 May and probably through the summer. 



Class II. — Oephalophora i W7iells, S .). 



General Characters of Cephalophores. — We now comi 

 M tllusks with a head bearing eyes and tentacles; but the 

 eral symmetry of the body, so well marked in the 

 elam. etc., is now in part lost, the animal living in a spiral 

 shell. Still the fool and head are alike on both sides of the 

 body; while the foot forms a large creeping flat disk by 

 which the snail glides over the surface of leave-, etc 

 Moreover, these mollusks have, besides two teeth, a " lingual 



