PULMONATA. 63 



The species is not uncommon ; but most generally casts only are found. In that 

 condition the wide umbilicus is the only character by which it can be separated from 

 H. Vectiensis. 



Diameter, 4-10ths of an inch nearly; elevation rather more than 2-10ths in. 



Localities. — Sconce and Headon-Hill. 



I have much pleasure in dedicating this species to my friend John D'Urban, Esq., 

 whose Palseontological pursuits have enabled him to add several interesting species to 

 our Eocene Fauna. 



No. 16. Helix globosa. Sowerby. Tab. X, fig. 2 a— d. 



H. globosus. Sow. 1818. Min. Con., vol. ii, p. 157, t. I/O. 

 — Morris. 1843. Cat. of Brit. Fos., p. 147. 



H. testa globoso-conoided, apice obtuso : awfractibus sex aut septem, transversim sub- 

 striatis, ultimo avfractu ad basin convexo ; striis numerosis, irregularibus, tenuissimis ; 

 suturis perspicuis ; aperturd depressd, semi-lunari, marginibus rejlexis ; columella sub-recta ; 

 umbilico obtecto. 



This well known shell is globosely conical, with an obtuse apex ; the spire is 

 formed of six or seven whorls, which exhibit obscure, transverse, irregular striae, or 

 lines of growth, so faint that, as Mr. Sowerby remarks, they are only to be seen in the 

 best preserved specimens. The base of the shell is very tumid, rising from the peri- 

 phery of the whorl with a bluntly convex swell until it nearly reaches the umbilicus, 

 into which it sinks abruptly, imparting an almost vertical slope to the columella. The 

 aperture in the adult shell is semilunate and depressed, with the margins reflected, that 

 of the inner lip entirely concealing the umbilicus. The young shell, like that of all the 

 globosely conical shells of this genus, presents a form very different from that of the 

 mature one. When in the young state, the whorls are subcarinated, increase rapidly 

 in size, and consequently are very convex, giving a sub-quadrate form to the aperture ; 

 and the shell presents a small umbilicus : but, as the shell approaches maturity, they 

 lose their sub-carinated form, increase in size more and more slowly, and become less 

 and less convex in their contour, so that, in the mature state, the aperture assumes a 

 semilunate form, and at this period of growth the umbilicus is concealed by the 

 reflected margin. 



Specimens with the shell preserved are extremely rare, but casts in all stages 

 of growth are comparatively common at Sconce Point. In the young state the 

 casts resemble those of Helix occlusa ; but the flattened base, the shorter and more 

 oblique columella, and the semi-ovate aperture, serve to distinguish the latter 

 species. 



I am indebted to Mr. Sowerby for the use of the original specimen described 



