S3 



HARDWICKE'S SCIENCE-GOSSIP. 



The upper face is nearly flat, while the under side 

 presents a moderately deep and wide concavity. The 

 aperture is transversely oval, and but slightly oblique. 

 The strice of growth are very conspicuous ; and 

 occasionally, although very rarely, the shells present 

 fine concentric lines, similar to those which char- 

 acterise P. euomphalus. In this species, however, 

 the lines are finer and more crowded, and seldom 

 extend beyond the first three or four volutions. The 

 fossil remains of this species abound in the Upper 

 Eocene beds at Sconce and Headon Hill, also at 

 Hordwell, Hants. 



Planorbis discus, Edwards. (Fig. 26, 4, a. b.) — 

 This well-marked species appears to be peculiar to the 

 fresh-water formation at Sconce, Isle of Wight. 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 suc- 

 ceeding one ; they are much flattened above, slightly 

 convex below, and obtusely rounded at the outer 

 edge. In the young shell, the inner margin is bent 

 rather abruptly towards the preceding whorl, and 

 presents an obtuse angle which defines the umbilicus, 

 similar to that presented by P. euomphahis and P. 

 rotiuidatus. As the shell becomes matured, the 

 under side assumes an almost regularly convex form, 

 and the angle becomes obsolete. The aperture is 

 oblique, and of an elongated heart-shape. Casts of 

 this shell occur in great abundance in the fresh-water 

 beds of the Upper Eocene formation at Sconce, Isle 

 of Wight. 



Planorbis digyratns, Edwards. — The present, like 

 the preceding species, is apparently confined to the 

 fresh-water formation of Sconce, but is not so plenti- 

 ful as P. discus. It is a moderate-sized shell, 

 formed of four rapidly-increasing whorls, somewhat 

 convex above, and rather acutely angulated round 

 the inner margins on the under side, just above the 

 umbilicus. The periphery, near the upper surface, 

 presents an obtuse angle, from which the whorls 

 shape rather abruptly towards the umbilicus, assum- 

 ing in consequence a subtrigonal form. The aperture 

 is slightly oblique, and bluntly obcordate in conse- 

 quence of its being impinged upon by the preceding 

 whorl. The umbilical cavity is deep, but not very 

 wide. 



This species is, in the fossil state, ordinarily 

 found as casts only, in the Upper Eocene beds of 

 Sconce, Isle of Wight. 



Planorbis platy stoma, Wood. (Fig. 26, b, a. b.)— A 

 small smooth shell, formed of three rapidly enlarging 

 whorls, each embracing about one-half of the pre- 

 ceding one ; the whorls are rounded, equally convex 

 above and below, but slightly compressed on the 

 upper side. The apex is wholly concealed by the 

 involutions of the whorls. The aperture is wide, 

 oblique, and bluntly heart-shaped ; the upper side is 

 slightly concave, and the under presents a wide and 



somewhat deep umbilicus. Planorbis platystoma is 

 found rather abundantly in the Upper Eocene beds at 

 Sconce, Headon Hill, and at Hordwell, Hants. 



Planorbis lens, Brongniart. (Fig. 26, 5, a, b.) — This 

 species is a small lenticular shell, slightly concave on 

 each side, but more so on the upper ; the whorls are 

 four in number, each embracing nearly one-half of 

 the preceding one ; they are also slightly convex on 

 both sides, but more so above than beneath, and 

 angulated round the periphery, a little below the 

 middle of the whorl. The aperture is heart-shaped, 

 but not very oblique. The fossil remains of this 

 species are found at Headon Hill, Isle of Wight, 

 and Hordwell, Hants, in the Upper Eocene forma- 

 tion. 



Planorbis tropis, Edward. — A minute shell, com- 

 pressed and polished, and slightly sunk round the 

 apex, and widely but not deeply umbilicated ; the 

 four or five volutions, of which it is composed, are 

 convex above and flat beneath, and compressed near 

 the outer margin so as to present a prominent keel, 

 which runs round the periphery a little below the 

 middle of the whorl. The whorls embrace one 

 another about one-half of the preceding one; the 

 aperture is very oblique, and of a longish heart-shape. 



This species seems to be peculiar to the Eocene 

 beds at Hordwell, Hampshire. 



Planorbis hemistoma, Sowerby. — P. kemistoma is a 

 minute, smooth, depressed shell, concave on the 

 upper side, almost flat beneath and compressed, 

 almost angulated at the periphery, above the middle 

 of the shell. The whorls do not exactly embrace one 

 another, although the upper surface is partly concealed 

 by the succeeding whorl ; the inner margin is bent 

 abruptly towards the apex, and presents a conspicuous 

 angle, which runs round the cavity. The aperture is 

 oblique and subtrigonal, having the lower margin 

 rounded. This species somewhat resembles P. 

 clegans, but is smaller and more compressed. 



Fossils of this species are found in the Eocene 

 formation at Hordwell, Hants ; Plumstead, Sund- 

 ridge, and Rotherhithe. 



Planorbis clegans, Edwards. (Fig. 26, 6, a, b.) — 

 This little planorbis is found in great abundance at 

 Headon Hill, Isle of Wight. It is a small polished 

 shell, deeply but not widely hollowed out on the 

 upper disc, and slightly concave, almost flat beneath. 

 It is composed of four or five volutions 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 a third of the 

 preceding one. The aperture is heart-shaped, and 

 slightly oblique. This species is found in the Eocene 

 beds at Headon Hill, Isle of Wight, and at Hord- 

 well, Hants. 



Planorbis biangulatus, Edwards. — A depressed, 

 small shell, slightly and nearly equally hollowed out 



