280 BRITISH KNTOMOSTKACA. 



Genus 4 — Trebius. 



Trebius, Kroi/ei\ Tidsskrift. 



— M. Edwards, Hist. Nat. Crust. 



— Thompson, Ann. aud Mag. Nat. Hist. 



Character.- — Fourth pair of feet slender, and divided 

 into two branches, adapted for swimming. Thorax pos- 

 sessed of three distinct articulations. Frontal plates 

 destitute of small sucking-discs or lunules. 



1. Trebius caudatus. Tab, XXXIII, figs. 8, 4. 



Tkebius caudatvs, Kroijer, Tidsskrift, ii, 30, t. 1, f. 4. 



— M. Edwards, Hist. Nat. Crust., iii, 458. 



— Thompson, Ann. and Mag. Nat. Hist., xx, 248. 



Description. — Female. Carapace nearly oval, rather 

 longer than broad. Frontal plates of considerable size. 



Antennae well developed ; setse on external edge of basal 

 joint plumose. 



Thorax narrow on first two joints, especially on second ; 

 last nearly quadrilateral, a little narrower at upper extre- 

 mity than lower, which is nearly straight on the edge. 



Abdomen long and narrow, nearly as long as the thorax, 

 slightly narrowed towards the centre, and terminated by 

 two small caudal appendages, which give off three long and 

 one short plumose setse. Sternal fork with simple branches. 



First pair of foot-jaws larger than in any of the Caligi, 

 and strongly hooked at their apex. Third pair much 

 smaller. Foiu'th pair of feet short, with basal joint broad, 

 and the two terminating articulations short, oval, and fur- 

 nished with several rather stout seta3. Oviferous tubes 

 short, and rather broad. 



Male. The male is much smaller than the female. Cara- 

 pace broader. 



Thorax, two first segments of much the same form as 

 in the female ; last joint somewhat hexagonal. 



