2 MOLLUSCA FROM THE CRAG. 



furnished 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 cal- 

 careous 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 sufficiently 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 

 greater 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 established, 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 Linnasus and other ancient authors, 

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

 sidered 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. 



— Midler. Verm. 11, p. 73, No. 268, 1774. 



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



— Rossmasler. 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. concinna. Jeffreys, Synopsis. 



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

 semilunari, labro tenui, sub-reflexa ; umbilico profunda. 



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, y 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 of H. plebeium 

 upon the tablet, which I think, however, is only a variety of //. hispida with a spire 

 rather more depressed, and an umbilicus a little larger. I have the same varieties 

 from Stutton and Clacton. This shell appears to present a slightly carinated form 

 in the young state, though not quite so much so in the middle of the volution as 

 in H. ru/escens ; this character is less distinct in the older specimens. 



