102 EOCENE MOLLUSCA. 
No. 53. PLANORBIS oBTUSUS. Sowerby. Tab. XV, fig. 1 a—e. 
PLANORBIS OBTUSUS. Sow. 1818. Min. Con., vol. ii, p. 91, t. 110, fig. 3. 
P. testd depressd, levi; superné convexiusculd, subtis concava: anfractibus quinis, 
obtusé-ovalibus, sese partim involventibus; suturis profundis : aperturd per-obliqua, obcordata. 
This very pretty shell has a smooth, shining, nearly polished surface ; it is depressed, 
nearly flat on the upper side, and moderately concave beneath. The volutions are five, 
separated by a deep suture, slightly convex on both faces, but rather more compressed 
on the under side than on the upper, obtusely rounded at the periphery, and each 
nearly half concealed by the succeeding volution. The aperture is very oblique and 
bluntly heart-shaped. 
In the general form and rounded whorls, this species much resembles P. sparna- 
censis (Desh.), but the whorls are not so numerous, and the aperture is more oblique. 
The lenticular form and angulated margin of P. /ezs, will prevent its being confounded 
with that species. 
Size.—Diameter, 7-10ths of an inch. 
Localities —Sconce ; Headon Hill; Upper mar., Hordwell. 
No. 54. Pranorsis piscus. F. 2. Edwards. Tab. XV, fig. 7 a—d. 
P. testd valde compressd, quinguies circumvolutd, superné pland, subtus profunde 
cavatd : anfractibus sex, rapide crescentibus, parum involventibus, subtus convexiusculis, ad 
marginem umbilicalem angulatis: apertura per-obliqua, elongato-cordata. 
This well-marked species appears to be peculiar to the fresh-water formation at 
Sconce. It is a much compressed discoidal shell, nearly flat on the upper side and 
deeply hollowed out below. The five or six whorls of which it is formed enlarge 
rapidly, and each is slightly embraced by the succeeding one; they are much flattened 
above, slightly convex below, and obtusely rounded at the outer edge. In the young 
state, the inner margin is bent rather abruptly towards the preceding whorl, and pre- 
sents an obtuse angle which defines the umbilicus, similar to that presented by P. 
euomphalus and P. rotundatus. As the shell approaches maturity, the under side 
assumes an almost regularly convex form, and the angle becomes obsolete. The 
aperture is very oblique, and of an elongated heart-shape. 
The species which most resemble the present are P. evomphalus and P. oligyratus. 
From the first of these, it is distinguished by its more compressed discoidal form, and 
the rounded periphery. The whorls also enlarge more rapidly, and are consequently 
fewer and broader; and they embrace more of the preceding one than do those of 
P. cuomphalus. The umbilical cavity also is not so wide. It is more difficult to 
