no 
BRITISH ENTOMOSTRACA. 
Superior antennae (f. 4 b) long and rather slender, 
and provided with two setae at their extremity, of con- 
siderable length. Inferior antennae or rami very large 
and powerful ; the basal joint is particularly so, and fleshy - 
looking ; the two branches are also large, and each divided 
into two articulations. Both articulations of posterior 
branch are nearly of equal size, the inferior having three 
and the upper eight long filaments springing from their 
inner edge. These filaments are not plumose, but are 
jointed at the middle of their length. The joints of the 
anterior branch are of unequal length, the first being long, 
and furnished with only one filament ; the second being 
very short, and sending off three long setae from its upper 
edge. 
The mandible (f. 4 /), labrum (f. 4 g ), oesophagus 
(f. 4 o ), and stomach (f. 4 a) are almost exactly the same 
as in Sida. 
The abdomen consists of a broad plate, with large knob 
and two long setae, and has two rows of short spines on 
its edge, as described in preceding genus. 
The feet also resemble those of Sida, and are six pairs 
in number. 
The male (t. XIV, f. 2) is smaller than the female, and 
is beautifully transparent. The antennules (f. 2 a) are 
long, with a tooth on the upper edge, about the middle 
of their length, and three long setae at their extremity. 
The abdominal plate (f. 2 b) appears to have a supple- 
mental plate, which covers it, and which is flat, broad, 
and curved at the lower extremity. 
The female has very few young, only two or three. 
The motion of this beautiful little animal is by sudden 
bounds, darting forwards, by means of its large rami, for 
a great distance at each bound. 
Hab . — Pond on the edge of the Colne, between Twick- 
enham and Whitton, Middlesex, July 1841 ; ditch near 
Richmond, opposite Isleworth, July 1841, August 1849. 
