MOLLUSC A. 91 



Physadre may have the same power. The passage to the next fiimily seems 

 to be through Gray's genus Chili na, which is a Limnea with fokls upon the 

 cohnnella. 



Fam. 6. AuricuJidce. In this monoicous family there are two tentacles, 

 and the eyes are at their external and posterior base. Some species inhabit 

 land, and others plants near the sea, and salt water marshes. Auricula inidcB 

 {pi. IQffig. 1) is the largest species of the genus, being four inches long, 

 and of a solid texture. 



Fam. 7. llelicidre. This family includes most of the nnmerous species 

 of land snails with an external spirivalve shell. All breathe free air, are 

 monoicous and inopei'culate, and have two large tentacles, with an eye upon 

 the apex, capable of being retracted by being turned within itself Besides 

 these, there is an inferior and smaller pair of tentacles present in most cases, 

 although in some of the minute species they have not been detected. Most 

 of the land shells of Europe and North America belong to Helix., a very 

 extensive genus, containing upwards of 500 species from various parts of 

 the globe, including the islands of the Pacific, all the continents, high 

 mountains, and cold climates, although the larger species are intertropical. 

 They vary in size from about a tenth of an inch to four inches. The 

 shells vary much in form ; the aperture is sometimes reduced to a narrow 

 fissure, or armed with teeth, in such a manner as to lead one to think it 

 impossible for the animal to get out or in. They hybernate nnder ground, 

 closing tlie aperture with a temporary operculum. Among the genera may 

 be mentioned BuUmus {pi. 75, Jigs. 93, 94), Clavsilia {jig. 100), which has 

 a peculiar operculum attached to the shell within the aperture, Pupa, 

 Sti'eptaxis, L*cc. Their food is fresh or decaying vegetable matter, and some 

 feed upon fungi. The large European sjDecies are cooked and eaten, and 

 the Pomans fattened them for the table. 



Fam. S. Limacidie. This family includes the naked snails without a 

 turbinated shell, but some of them have an internal shell, or a small external 

 one which is little more than an appendage. The head, tentacles, organization, 

 habits, and food, do not differ essentially from those of the preceding family. 

 The genus Limax {pi. 71, figs. 19-21) is destructive to the plants cultivated 

 by the farmer and gardener in Europe, and new modes of destroying them 

 are continually sought after. The species which occnr in North America 

 have not yet proved injurious, and the same remark applies to the snails, 

 which are troublesome to gardeners in Europe. The body of Limax is 

 very contractile, but when moving on its lower surface or foot, it is rather 

 slender, thickest in the middle, and tapering towards the extremity. Upon 

 the back is a kind of fleshy shield, beneath which the head can be drawn. 



Class 3. CepJialopoda. 



This class was named MalaMa by Aristotle, and Mollia by Pliny. It 

 includes certain dioicous marine mollusca, which have the feet or arms 

 around the mouth at the extremity of the head. The body is soft, the 



295 



