108 EOCENE MOLLUSCA. 



No. 61. Planorbis biangulatus. F. E. Edwards. Tab. XV, fig. 13 a — d. 



P. testa parvd, compressiusculd, utrinque par urn, sed fere equaliter cavatd: anfractibus 

 quints, singulo antecedentem pauxillulo involventi; supra convexis, ad marginem sinistram 

 angulatis ; subtus convexiusculis, ad marginem externam obscure cremdatis: aperturd irre- 

 gulariter obcordatd, vix obliqud. 



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. Planorbis Sowerbyi. Bronn. Tab. XV, fig. 9 a — d. 



Planorbis Soweubyi. Bronn, 1838. Lethsea geognost., p. 1011, t. xl, fig. 17 a — c. 



P. testa parvd, depressd, utrinque parum etfere equaliter cavatd: anfractibus ternis vel 

 qnaternis, rapide crescentibus ; supra convexis, infra subplanis, ad periplieriam carinatis, 

 singulo dimidium antecedentis obtegenti, carina inferiori; aperturd elongato-cordatd, 

 per-obliqud. 



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. lens, and to have been correctly 



