122 LIMNAID. 
8. P. CARINATUS (eeled) Miller. Pl. VI., f. 8. 
Compressed, sfzve sunk, only slightly convex beneath, slightly 
glossy, semi-transparent, pale brown; worls 5 to 6: seture deep; 
mouth angulated above and below; sharply keeled in the ceztre of 
the outer margin. A. 33mm. B. 13 mm. 
Found in the south and east of England, in Lancashire; 
south of Scotland, being confined to one locality in 
Edinburgh, in a pond in the Botanic Garden, where it 
was probably introduced ; in Wales, and Ireland; but it 
is local, and not often plentiful. 
Var. I. disceformis ( Jef.). Flatter and thinner. 
Var. Il. dlbida (Hudson). White. 
9. 7 P. UMBILICATUS A/uller. - Pl. VI., f. 9. 
[=P. compLanatus Jeffreys]. 
Concave above, flat beneath, nearly opaque; strongly keeled 
below ; whorls 5—6; mouth rhomboidal. A. 33mm. 5B. 15 mm. 
This species is often very like the last on account of 
the position of the keel being higher than in type speci- 
mens ; indeed there is some doubt as to the actual specific 
distinction between the two species. Dissection has 
hitherto failed to find a difference in the animals. The 
young shells are not always keeled and they then some- 
what resemble P. parvus. 
It has a somewhat wider distribution throughout the 
British Isles than the last species, and it is more common. 
The largest specimen I have seen, is one that I took near 
Maidenhead, measuring 18 mm. across. 
