X HRIT1SH SHELL-BEARING MOLLUSCA. 



surface. Mangelia, 4-26, has a similar long siphon. The shell of 

 Erato, 27, is wrapped in the lobes of the animal's mantle, as is also 

 that of Q/prea, 28, the latter presenting a beautiful object. 



Plate XX. 



After Tornatella, 1, and Ovula, 2, 3, come Bullidce, 4-27, including 

 several genera differing remarkably in the shape and disposition of the 

 lobes of their mantles, which in some instances, as in Philine, 20-25, 

 cover the shell. The stomach of Scapander, 26, 27, is a remarkable 

 kind of mill, composed of two bones, between which the food is 

 ground. The shells of Aplysla, 28, and Pleurotranchus, 29, 30, are 

 quite internal. Spirula, 31, belonging to the Cephalopodous or Cuttle- 

 fish tribe, is only introduced doubtfully, as there is no proof of the 

 species living in our seas. 



Plates XXI., XXIL, XXIII., XXIV. 



These are occupied by shells of Gasteropoda pulmonifera, so named 

 because they breathe air by a pulmonary cavity, instead of water by gills. 

 The Limnceada, or fresh-water Snails, contained in Plate I., live in water, 

 but breathe by exposing the pulmonary cavity to air at the surface. 

 Succinea, Plate XXIL, 1-3, lives by the sides of streams, sometimes 

 immersed. Conovulus, 4-7, affects brackish marshes. Our common 

 Slugs yield, on dissection, thin shells, which are concealed beneath the 

 mantle, Limax, 9-12. The shells of Testacellus, 13, 14, are fixed 

 near the end of the foot, outside. The glassy shells of Vitrina, 15, 16, 

 do not enclose the whole Slug-like animal. The other genera of Land 

 Snails have shells large enough to receive the animal when retracted 

 and withdrawn for repose. 



