PLANORBIS. 31 
7. P. vOrTEX (whirlpool). 
Very flat, glossy; yellowish horn-colour; whorls six to 
eight ; sharply keeled. 
Found in similar habitats to the last species, but is 
less common. I have noticed that it is much more 
often found with a perfect epidermis than P. spzrorbis, 
even in the same pond as that species. 
It may be distinguished from P. spirorbis by its 
prominent keel ; it is also flatter and thinner. 
Var. compressa. Thinner and much flatter, and 
more sharply keeled. 
8. P. carmnatus (keeled). 
Compressed, spire sunk, only slightly convex beneath, 
slightly glossy, semi-transparent, pale brown; whorls five 
_to six; suture deep; mouth angulated above and below; 
sharply keeled in the centre of the outer margin. 
Found in the south and east of England, in Lan- 
cashire, south of Scotland, in Wales, and Ireland ; 
but it is local, and not plentiful. 
Var. disciformis. Flatter and thinner. 
9. P. comMPLANATUS (flattened). 
Concave above, flat beneath, nearly opaque, strongly 
keeled below; whorls five to six ; mouth rhomboidal. 
This species is often so like the last that a very 
