WATER SNAILS. 
217 
length, of which is about one-third the diameter 
of the shell. The animal, when walking in the 
water, carries the shell inclined at an angle of 
from 70° to 80°. 
The shell is finely striated longitudinally; the 
epidermis is raised into deciduous bristles on the 
striations, also minutely striated transversely; 
convex above and below, thin, pellucid, and 
whitish; about one-fourth of an inch in diameter; 
the whorls five, the last one disproportionately 
enlarged. 
It is a common species. 
Planorbis glaber— {the Smooth Coil Shell) (PI. 
XI., fig. 126).—The nearest ally to this species 
is P. albus , from which it differs in its smaller 
shell, which is smooth; in the more rounded 
whorls, the npper side being more convex; and, 
lastly, in being destitute of the strong spiral 
striae. 
P. glaber was first described by Mr. Jeffreys, 
who states that he only knows about twenty 
localities for it in England and Scotland; it is 
rather a northern than a southern form; it has 
been found in the neigbourhood of Belfast, Ire¬ 
land, and in three other localities in the north¬ 
east of the island. It is distributed throughout 
the greater part of the continent, and ranges 
from Sweden to Corsica and Algeria. 
Planorbis nautileus —[the Nautilus Coil Shell) 
