o+ LAND AND FRESH-WATER MOLLUSKS. 
~ 
Berkeley, and Combe Hill Canals, Gloucester- 
shire ; Oxford; Chester; York; Doneaster; &c. 
lt is a species of the newer Tertiaries. 
Cyctas cornzra—(the Horny Cyclas) (PI. III., 
fig. 18).—The shell of this species is not more 
than half the size of the last, and more globular ; 
its length about six lines, breadth four, and thick- 
ness three and a half; equilateral, finely striated 
concentrically, of a yellowish-brown colour, with 
paler bands ; ligament indistinct externally. 
It varies very considerably: there are three 
well-known varieties.—1. var. jlavescens (PI. IIL., 
fig. 16), with a smaller and rounder shell, the 
body and shell straw- or lemon-coloured. 2. 
Which is probably the fry of C. cornea, with a 
small, nearly globular shell. 3. Gibbous at the 
beaks, but thin or compressed towards the edges. 
Few pools, ditches, or streams throughout the 
United Kingdom are without this very interesting 
bivalve. In summer it is found among the con- 
fervee floating near the surface of the water; in 
winter it buries itself in the mud. 
No aquarium can be considered at all complete 
without this interesting animal, whose habits are 
so much at variance with the popular notions re- 
garding the way in which mussels, cockles, and 
other bivalves pass their days. It crawls readily 
by the aid of its long foot, or ascends the sides 
of the glass, and, on reaching the surface, moors 
a a el nn 
