PULMONATA. 107 



usculis, ad marginem sinistram acute angulatis; infra subplanis; aperturd parum obliqud 

 subtrigond. 



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. biang/datus, the whorls are more convex, and the aperture is consequently almost 

 obcordate. 



Size. — Diameter, 1-1 Oth of an inch nearly. 



Localities. — Hordwell ; Plumstead ; Sundridge ; Rotherhithe. 



No. 60. Planorbis elegans. F. E. Edwards. Tab. XV, fig. 12 a — d. 



P. testa minutd, politd, superne profundi; cavatd, subtus parum cavatd; quater vel 

 quinquies circumvolutd, anfractibus lineis incrementi notatis, ad peripheriam rotundatis ; 

 supra convexis, ad marginem sinistram angidatis ; infra convexiusculis ; singidofere trientem 

 antecedentis obtegenti : aperturd parum obliqud, obcordatd. 



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 Bulimiis 

 politus, Melanopsis carinaius, Melanopsis buccinoidea, a species of Neritina, as yet 

 undescribed, and Melania 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. 



