518 



ZOOLOGY. 



lodged between the mantle and the foot, or even on the back 

 of the animal, so as to float freely in the surrounding liquid; 

 as an example of the pulmonary gasteropodes, we may men- 

 tion the slug and snail, which live on the land ; the lymnseus 

 or helix (Fig. 166), the planorbis (helix vortex), and the 



Fig. 542. Eolis. 



physa (the helix fontiualis), which live in stagnant waters, and 

 ascend to the surface to breathe the requisite air. Amongst 

 the gasteropodes provided with gills enclosed in a dorsal 

 cavity may be observed the volutes, the buccinures, the por- 

 celaines (Fig. 181), the heliotides, &c. The patellae and the 



Fig. 543. Carinaria.* 



pleurobranchiaB (Fig. 541) carry these organs in the furrow 

 separating the foot from the mantle; and in the doris and the 

 eolis (Fig. 542), &c., they consist in bunches and in straps or 

 leashes fixed on the dorsal aspect of the body. 



* b, mouth ; t, tentacles ; y, the eyes ; e> stomach ; f t liver ; a, anus ; c, 

 shell; br, gills; p, the foot; v, ventouse (cupping-glass-cavity air hole) 

 situated under the edge of the foot. 



