PLANORBTS. 61 



P. GLABER. Jeffreys. PL VII, fig. 21. 



Shell small, whorls equally convex on both sides, round and promi- 

 nent, the outer one not keeled. 



Planorbis Isevis, Gray, S^c. 



This little shell somewhat resembles the foregoing, 

 but may be readily distinguished by being smaller, 

 about one-fifth of an inch in diameter, and having the 

 whorls much closer set, and more rounded, especially 

 on the upper disk. It is also destitute of the spiral 

 striae or hairs. 



Hah. Though generally distributed it is somewhat 

 local. It is found in similar habitats to the preceding. 

 It occurs in Cornwall and the south of Wales, Ox- 

 fordshire and the adjacent counties, Staffordshire and 

 Somersetshire, JSTorth Stainley, near Eipon, and at 

 Ackworth, near Pontefract, in an old depopulated fish- 

 pond, on Potomogeton crispus. It has also been met 

 with in other places in Yorkshire, Durham, and JSTorth- 

 umberland. 



P. NAUTiLEUS. Linnceus. PI. VII, fig. 23. 



Shell minute, with numerous transverse ridges; whorls depressed 

 and keeled ; aperture oval. 



Planorbis imbricatus. Mull., Sfe. 



A beautiful little shell, and may be readily distin- 

 guished by the spinous ridges on the outer whorl. 

 From an eighth to a tenth of an inch in diameter. The 

 shell is of an olivaceous horn colour, often covered 

 with a darker epidermis, not polished. Whorls from 

 three to three and a half, which are well defined. 

 Animal pale grey. 



Hah. Somewhat local, though generally diffused, 

 and in some places abundant. It prefers stagnant 

 water in ponds, ditches, &c., generally adhering to 

 aquatic plants, often in colonies. Ponds near Ack- 

 worth, in profusion, ditches near Middlesbro', &c. It 

 occurs in most parts of Ireland. 



P. CARiNATUs. Muller. PI. VII, fig. 24. 



Shell horn coloured, somewhat transparent and polished, nearly 

 smooth, strongly carinated. 



