PULMONATA. 107 
usculis, ad marginem sinistram acute angulatis; infra subplanis; aperturd parum obliqud 
subtrigonda. 
A minute, smooth, much depressed shell, deeply concave on the upper side, almost 
flat on the under side: volutions three or four, very slightly convex above, nearly flat 
beneath, and compressed, almost angulated at the periphery above the middle of the 
shell. The whorls can scarcely be described as embracing, inasmuch as the under 
surface is wholly exposed, although the upper surface is partly concealed by the 
succeeding whorl; the inner margin is bent, rather abruptly, towards the apex, and 
presents a conspicuous angle, which runs round the cavity. The aperture is oblique, 
but not much so, and subtrigonal, having the lower margin rounded. 
This species somewhat resembles P. elegans; but it is smaller and more compressed, 
and the subangulated periphery and flatness of the whorls impart a triangular form to 
the aperture very different from the roundish, heart-shaped aperture of that species. 
In P. biangulatus, the whorls are more convex, and the aperture is consequently almost 
obcordate. 
Size—Diameter, 1-10th of an inch nearly. 
Localities—Hordwell; Plumstead; Sundridge; Rotherhithe. 
No. 60. PLANORBIS ELEGANS. J. LZ. Edwards. Tab. XV, fig. 12 a—d. 
P. testd minuta, politd, superne profunde cavatd, subtus parum cavata ; quater vel 
quinquies circumvolutd, anfractibus lineis incrementi notatis, ad peripheriam rotundatis ; 
supra convexis, ad marginem sinistram angulatis ; infra convewxiusculis ; singulo fere trientem 
antecedentis obtegenti: apertura parum obliqud, obcordatda. 
This very elegant little Planorbis is found in great abundance on Headon Hill, in 
a deposit immediately above the upper fluvio-marine formation, associated with Bulimus 
politus, Melanopsis carinatus, Melanopsis buccinoidea, a species of Neritina, as yet 
undescribed, and AZelania muricata. It is a small polished shell, deeply but not widely 
hollowed out on the upper disc, and slightly concave, almost flat, beneath: volutions 
four or five, rounded on the periphery, marked by conspicuous lines of growth nearly 
perpendicular to the axis, very convex, and presenting a sharpish angle running round 
the inner margin, on the upper surface, and but slightly convex beneath ; each volution 
embraces nearly a third of the one preceding it. The aperture is of a roundish heart 
shape, and very slightly oblique. 
Size.—Diameter, 3-20ths of an inch. 
Localities—The deposit in which this Planorbis principally occurs is a transition 
bed between the upper fluvio-marine and the pure fresh-water formations in Headon 
Hill. I have also found it, but very sparingly, in the upper fluvio-marine formation 
at Hordwell, and in the lower fluvio-marine or transition bed which intercalates the 
upper series of the true marine and the lower fresh-water formations at Mead End. 
