PLEUROXUS. 
135 
Abdomen (t. XVII, f. 3 c) gibbous for latter half, and 
serrated. 
First pair of feet (f. 3 b) very large ; the pediform organ 
of Muller being the first pair of feet. 
Intestine convoluted, having one turn and nearly half 
another. 
Hah . — Pond near Copenhagen Fields, Osterly Park, 
Norwood Green, and Southall, Middlesex, June to 
October. Pond at Fouldean, Berwickshire ; and at 
Yetholm, Roxburghshire. ^ ~ 
2. Pleuroxus uNciNATUs. Tab. XVII, fig. 4. 
Shell slightly triangular in shape, transparent, and 
fluted; gibbous on upper portion of anterior edge, and 
less straightly cut on lower portion of anterior edge 
than in preceding species. At the inferior angle of this 
margin there are three sharp spines, and the margin itself 
is ciliated. The posterior margin is rounded and sinuated 
at the lower part, but not so deeply as in trigonellus , 
and the square point at extremity is shorter than in it. 
The beak is long and curved ; but the tip, instead of 
being curved downwards as in preceding species, is 
turned up. 
The antennules, antennae, feet, and abdomen, with in- 
testine, are similar to those parts in trigonellus , and the 
animal is nearly of the same size. 
The ova, in all the specimens I have met with, are only 
two. 
The young exhibit the remarkable turned-up beak and 
the spines on inferior extremity of shell as soon as born. 
Hab . — Pond between Han well and Southall, Middlesex, 
September 1849. 
