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 
HT. 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 Paleontological pursuits have enabled him to add several interesting species to 
our Eocene Fauna. 
No. 16. Hetix Gtosposa. Sowerby. Tab. X, fig. 2 a—d. 
H. ctoposus. Sow. 1818. Min. Con., vol. ii, p. 157, t. 170. 
— Morris. 1843. Cat. of Brit. Fos., p. 147. 
H. testd globoso-conoided, apice obtuso: anfractibus sex aut septem, transversim sub- 
striatis, ultimo anfractu ad basin convexo; striis numerosis, trregularibus, tenuissimis ; 
suturis perspicuis ; apertura depressd, semi-lunari, marginibus reflexis ; 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 striee, 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 
