ZOOLOGY. 



inhabit the sea, some fresh waters, and others are met u ith 

 on land, the most valuable marine species are fished up from 

 deep waters, or found adhering to rocks and stones below 

 high- water mark. This is a very extensive genus, and a 

 very considerable number are found on the British shores. 



29. Helix, Snail. lohabilant a Slug. 



Shell spiral, thin, brittle, almost transparent ; aperture 

 semi-lunar or circular. Plate 5, fig. 29. There are five 

 families of this genus : * Whorls^ compressed, or 

 acutely carinate : Umhilicate^ whorls rounded : 



Imperforate^ whorls rounded : Tapering : 



***** Ovatey imperforate. 



Of the land species, almost every place produces some 

 one or other of the kinds, they are found on frees, wails, 

 moist mossy banks, under stones, &c.; of the Aquatic spe- 

 cies, some are found on tlie sea shores, on the banks or 

 margins of rivers, brooks, and ponds, but mostly in shallow 

 "waters, the whole are of very brittle substance, and exceed- 

 ingly susceptible of injury. Some of the kinds are used as 

 food ; the species are ver^ numerous, nearly seventy, being 

 found in Great Britain. 



30. Nerita. Nerite. Inhabitant a Limax. 



Shell spiral, gibbous, somewhat flattened beneath ; aperture 

 semi-orbicular, with the columella uniformly strait. 

 Plate 5, fig. 30. There are three divisions of this genus: 

 * JJmbilicate : ** Imperforate^ with the lips tooth- 

 less : *** Imperforate, with the lips toothed. 



