UNIVALVE S. 
59 
and widely - distributed species, very abundant 
on tbe bottoms of shallow muddy streams, on 
marsh lands, or on aquatic plants in ditches and 
canals. 
Mr. Benson some years since favoured me 
with what appeared to be a shell of this species; 
but, strange to say, it was the house of a South 
American species of caddis-worm. The domicile 
was a perfect imitation of the shell of our little 
V. piscinalis, and of the same size. The mate¬ 
rials of which it is constructed are not the less 
singular. The spiral valvata-like tube was of 
the ordinary secreted matter, to which were 
affixed remarkably fine grains of sand ; and for 
an operculum the scale of a fish was ingeniously 
appropriated. 
Valvata cristata — (the Crested Valve-shell) 
(PI. II., fig. 6)—is a minute species, living on 
the aquatic vegetation of lakes, ponds, canals, 
and ditches; and though it is widely diffused 
throughout our islands, is by no means a 
common species. The shell is flat, like that 
of a Planorbis, but easily distinguished from 
it by the continuous margin of the aper¬ 
ture, being circular, like that of F. piscinalis , 
for which it could never be mistaken; for in all 
stages of growth the shell of this species is flat 
above, whereas that of V. piscinalis is more or 
less globular. The shell is only one-tenth of an 
