60 LIMNJEAD^E. 



Helix cornea, Mont., fyc. 



This largest of our British Planorbes cannot possibly 

 be confused with any other on account of its superior 

 size, often measuring one inch in diameter, and one- 

 third of an inch in height. The shell is strong, 

 generally of a rusty brown or olivaceous yellow colour; 

 it is closely and obliquely striate. The animal is nearly 

 black, and when irritated gives out a purple fluid. 



Hob. This elegant shell seems to hold a similar posi- 

 tion among the Planorbes, to that of H.pomatia among 

 the Helices, both being considerably larger than any 

 other species belonging to the same genus. It is abun- 

 dant in canals, ponds, slowly-running streams, &c., in 

 all parts of the south of England, with the exception 

 of Cornwall and Devon. It is recorded as having been 

 found as far north as Darlington. It occurs in one or 

 two localities towards the south of Yorkshire and Lan- 

 cashire. It has been found in Ireland. 



P. ALBUS. Mutter. PI. VII, fig. 27. 



Shell small, white or nearly so; slightly convex on both disks, 

 whorls nearly striated and pilose. 



Planorbis hispidus, Drap., fyc. 



This pretty little shell may be instantly detected 

 when quite fresh by its downy appearance, being 

 covered with minute hairs, which fall off with the epi- 

 dermis. It is the only British fresh-water species that 

 is at all hispid. The shell is thin, not much polished ; 

 the upper surface a little sunk in the middle, the lower 

 still more concave; rather angularly rounded at the 

 periphery ; about a quarter of inch in diameter. 

 Generally a pale horn colour, but sometimes, particu- 

 larly old specimens, more or less white. Animal a 

 pale grey, but varies in different localities. 



Hob. Stagnant waters upon aquatic plants, Pota- 

 mogeton in particular. It is widely distributed, and 

 may be found more or less sparingly in almost every 

 locality. We have met with them occasionally in 

 several stells, in the neighbourhood of Ayton. 



