77 
VIVIPARA fluviorum. 
TAB. XXXI.— Fig. 1. 
Spec. Char. Volutions four to six,, convex. Shell 
about twice the length of the aperture. Lines 
of growth rather sharply conspicuous, giving 
the shell a finely striated appearance. 
Shell not quite twice as long as broad. When full grown, 
about an inch and an half long, and seven-eighths wide. 
Of the three central figures above the slab, the upper two 
are filled with a loose kind of marie, the shell being replaced 
by a dark coloured imperfectly crystallized Carbonate of 
Lime, in part bleached externally, so as to look like the sun 
dried remains of the recent Vivipara fluviorum; the lower 
figure is from a recent specimen, for comparison, from the 
centre of a pond that has been dried up. The figures on 
either side of these differ in the length of the spire, but I can 
only consider them as varieties, for there are several inter- 
mediate ones among the specimens from which the figures 
are selected ; the recent shells are subject to the same varia- 
tions, the larger and longer ones being generally found 
in the deepest water, as in the Thames and some deep 
ponds at Hackney. These were presented to me, some by 
Mr. R. Weeks, and others by the Rev. Mr. Fearon; they 
are brought from Sussex*. 
* I saw a large mass full of shells like these in the Bishop of Winchester’s 
Park at Farnham ; it had been picked up in the neighbourhood. Wapping 
Docks also afforded this shell while digging. 
