4 MOLLUSCA FROM THE CRAG. 



reflected or thickened, more especially at the lower and inner part of the mouth. The 



perfectly smooth appearance of the specimen is in all probability the result of attrition. 



A recent specimen from Ayrshire, much depressed in form, has been obligingly sent 



me by Wm. Thompson, Esq., of Belfast, which very strongly resembles our Crag shell. 



4. Heltx rysa. S. Wood. 1847. Tab. I, fig. 1. 



II. Testa orhicidato-depressd, perforata, supra convexd, radiatd, rugosd, sen corruyatd ; 

 mhtm rotundatd, profuiide umbilicatd et subtilissime striata; anfractihus septern ohtme 

 carinatis, carinis prope suturam dist'uictis : aperturd subdepressd, late lunari ; peritremate 

 acuta, rejlexo. 



Shell orbiculato-depressed, perforated, convex, rugosely striated, or rather corru 

 gated, on the upper half of the volutions, rounded, and faintly striated on the under 

 surface, with a large and deep umbilicus ; volutions seven, obtusely but distinctly 

 keeled; keel visible at the suture on the upper side ; aperture broadly lunate, with a 

 sharp and reflected peritreme. 



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



Locality. Red Crag, Walton Naze. 



The elegant and, as far as I know, unique specimen, from which the figure above 

 referred to was taken, is from the cabinet of G. S. Gibson, Esq., of Saffron Walden, 

 who has kindly intrusted me with this rarity for publication. It was found, he 

 informs me, in the interior of a specimen of Buccinum undatmn. 



By careful examination, as well as by the assistance of my conchological friends, I 

 have been unable to find a species with which this could be identified. In comparing 

 it with II. rvfescens, the shell to which it appears to have the greatest affinity, some 

 essential differences exist ; it is rather larger, and has seven volutions, whereas in that 

 species I have never been able to obtain a specimen with more than six ; it is more 

 distinctly and roughly corrugated on the upper surface, and the keel, though obtuse, 

 is visible up the spire ; the lines of growth are not more prominent upon the under 

 surface than those upon H. rufescens, where there is a strong resemblance between 

 the two. In this the aperture is of the same form, though the peritreme is rather 

 more reflected, and a little depressed at the suture. 



Cyclostoma,* Lam. 1799. 



Cyclostoma elegans. Brap. 



Specimens of this well-known species are found in the upper part of the Coralline 

 Crag, as well as oiHelix crystulJina,Pnpamarginuta, and Cyrena triyomda, in association 

 with marine species. The locality from which they were obtained is rather a douljtful 

 one, and from their very recent aspect they must, at least for the present, be considered 



* Etym. Ki/)c\os, a circle, and oro^ia, a mouth. 



