108 EOCENE MOLLUSCA. 
No. 61. PLANORBIS BIANGULATUS. F. F. Edwards. Tab. XV, fig. 138 a—d. 
P. testé parva, compressiusculd, utrinque parum, sed fere equaliter cavatd : anfractibus 
quinis, singulo antecedentem pauxillulo involventi; supra convexis, ad marginem sinistram 
angulatis ; subtus convewiusculis, ad marginem externam obscure crenulatis: apertura wre- 
gulariter obcordata, vie obliqua. 
A small, somewhat depressed shell, slightly and nearly equally hollowed out on both 
sides, but rather more so above than beneath. It is formed of four or five volutions, 
convex on the upper side, and obtusely angulated round the cavity in consequence of 
the somewhat abrupt inflection of the inner margin toward the preceding volution ; 
nearly flat on the under side, and obscurely crenulated near the outer margin. The 
periphery presents two angles; one, rather obscure, near the middle; the other, more 
prominent, runs round the margin of the lower disc. The aperture is slightly oblique, 
and of a short heart shape, but irregular in its form, owing to the greater convexity 
and the angulated inner margin of the upper surface of the whorl. 
This appears to be a well-marked species; the double angle on the periphery and 
the crenulated under surface are characters which are not found in any other of the 
Eocene species. 
Size.—Diameter, 2-10ths of an inch. 
Localities—Hordwell, as well in the pure fresh-water, as in the upper fluvio-marine 
formation; and at Mead End, in the lower fluvio-marine or transition bed before 
mentioned. 
No. 62. PLaNnorBIs SowERBYt. Bronn. Tab. XV, fig. 9 a—d. 
PLANoRBIS SoWERBYI. Bronn. 1838. Letheea geognost., p. 1011, t. xl, fig. 17 a—e. 
P. testd parva, depressd, utrinque parum et fere equaliter cavata : anfractibus ternis vel 
quaternis, rapide crescentibus ; supra convewis, infra subplanis, ad peripheriam carinatis, 
singulo dimidium antecedentis obtegenti, carind inferiori; apertura elongato-cordatd, 
per-obliqua. 
The present species appears to be rare. It is a small depressed shell, slightly and 
nearly equally hollowed out on both surfaces; but the umbilical cavity is the wider 
and deeper of the two. The volutions are three or four, enlarging rapidly, convex 
above, nearly flat beneath, and bearing a sharpish keel on the periphery, formed by 
the compression of the outer margins, a little below the middle of the shell. The 
whorls are much concealed, each embracing nearly half of the preceding one, and the 
aperture is very oblique, and of an elongated heart shape. 
This shell appears to me, as I have already stated, to have been mistaken by 
M. Bronn for that described by Mr. Sowerby as P. /ens, and to have been correctly 
