2 MOLLUSCA FROM THE CRAG. 



nishcd with a simple pulmonary cavity, situated beneath the edge of the mantle, on 

 the right side of the animal ; most of them are covered and protected by a calcareous 

 shell, more or less convolute. Those which are constant inhabitants of the water, 

 come occasionally to the surface for a supply of air, a necessary and vital element, 

 which they cannot suflSciently obtain from the water alone. 



As the species of this genus are entirely terrestrial, the presence of specimens 

 found associated with marine shells in the Mammaliferous Crag may be due to the 

 transporting power of rains and floods, conveying them into the ancient estuary, and 

 to their buoyancy (more especially if dead shells) permitting them to be carried to 

 o-reater or less distances, before they become entombed with the marine exuviae. 



Upwards of a hundred synonyms are given by Hermansen to this genus as originally 

 estabhshed, many authors conceiving a very slight alteration of character sufficient to 

 constitute generic distinction. 



A genus like the present, which, even when shorn of all those marine, fluviatile, 

 and terrestrial forms that were included in it by Linnaeus and other ancient 

 authors, contains in a living state, nearly one thousand species, might, however, be 

 considered as deserving of subdivision, were it only to assist the student in the difficult 

 task of investigation. 



1. Helix hispida. Linn. Tab. I, fig. 3, a — c. 



Helix hispida. Lin. Syst. Nat. p. 1244, 1766. 



— MuUer. Verm. 1 1, p. 73, No. 268, 1774. 



— Mont. Test. Brit. p. 423, t. 23, fig. 3, 1803. 



— Riissmasler. Iconog. t. 31, fig. 426-427, 1835. 



— Gray. 2d edit, of Turt. Man. p. 154, t. 4, fig. 51, 1844. 



— S. Wood. Catalogue 1842. 



— var. eoucinna. Jeffrexjs, Synopsis, 



H. Testa orbiculato-convexd; spird depressd, anfractibus 4 — 5 vix carinatis; aperturd 

 semilimari, labro tenui, mb-reflexa ; umbilico prof undo. 



Shell orbiculato-convex, with a somewhat depressed spire ; whorls four or five, 

 slightly carinated ; aperture semilunate, with a moderately sized, and deep umbilicus. 



Diameter, \ of an inch ; elevation, \ ditto. 



Locality. Mam. Crag, Bulcham. Recent, Britain. 



Several specimens have been kindly lent to me for comparison, from these, with a few 

 of my own, I have no hesitation in assigning this to H. hispida. Two varieties are among 

 those belonging to Mr. Lyell, one of which has the name oi H. plebeiim upon the tablet, 

 which I think, however, is only a variety of H. hispida with a spire rather moi-e de- 

 pressed, and an umbilicus a little larger. I have the same varieties fi'om Stutton and 

 Clacton. This shell appears to present a slightly carinated form in the young state, 

 thougli not quite so much so in the middle of the volution as in //. rufescens ; this 

 character is less distinct in the older specimens. 



