110 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 fmiiished 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 ^), oesophagus 

 (f. 4 d), 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. 



