58 LINN^AN GENERA. 



aperture angulated, and slanting towards the base. Inhabits 

 ponds, rivers, and ditches in Britain. 



Helix subulata The Awl-Shaped Helix. Plate III. 



fig. 7- (Pyramis subulatus, Brown.) Shell tapering and 

 subulate, very smooth, and glossy; whorls about ten, and 

 scarcely defined ; colour white, with two pale-chestnut 

 spiral lines running from the body to the apex, becoming 

 very faint on the upper whorls; aperture ovate, and rather 

 contracted. Length three quarters of an inch. Inhabits 

 the sea at Weymouth, the Frith of Forth, and the coast of 

 Aberdeenshire. 



D Spire, F body, o pillar-lip. 



Habitation. The Helices are found in the ocean, in lakes, rivers, 

 and on the land. They are inhabitants of almost all countries of the 

 globe, and are in genei'al very numerous. On land they are found to 

 inhabit trees, old walls, mossy banks, and rocks, as well as under stones. 



The animals of this genus are termed snails in Britain ; they feed on 

 vegetables. It has been asserted, and on apparently good authority, 

 that snails have been known to revive after remaining in torpidity fur 

 a number of years ; snails are possessed of very considerable repro- 

 ductive powers, and are capable of reproducing the head after it is 

 taken off. 



Genus 30.— NERITA. 



Animal a Limax ; shell univalve, spiral, gibbous, flattish 

 at bottom ; aperture semi-orbicular, or semilunar ; pillar- 

 lip transversely truncate, flattish. 



This genus is divided into three families: *umbilicate ; **imperfo- 

 rate, with the hps toothless ; ***imperforate, vnt\x the lips toothed. 



Nerita Uttoralis — The Shore Nerita. Plate IX. fig, 

 30. (Neritoides littoralis, Brown ) Globular, thick, smooth ; 

 spire flat; yellow, covered with an olive epidermis, beneath 

 which the shell is either yellow, orange, or red, frequently 

 with elegant zigzag lines of red or brown. Three-fourths 

 of an inch long. Inhabits the British coasts. 



The Neritae inhabit the sea, lakes, and rivers. The marine species 

 are found near the shore, and several are attached to marine plants ; 

 some are only found in deep water so that live specimens can only be 

 had by trawling for them. 



