344 Ori Aquatic Carnivorous Coleoptera or Dijtisci'a'. 



I. 22.— Genus BIDESSUS. 



Prosternal process longer than broad, parallel-sided, but with a more or less 

 acute extremity which attains the metasternum ; intercoxai process of metasternum 

 not attaining the mesosternal fork, so that when the prothorax is taken away it may 

 be seen that the middle coxfe touch one another ; posterior tibire with the basal 

 portion much more slender than the apical one. Cosal lines longer than prosternal 

 process. 



These insects are of small size, (2 or 3 m.m. long.), and are found in most parts 

 of the world. 



More than 80 species are included in this genus * ; this renders it necessary that 

 an arrangement of the descriptions should be made to facilitate reference ; and in 

 order to do this as naturally as possible, I have separated from the bulk of the 

 species four natural groups, and left together the remainder of the genus in one 

 group, which I have artificially divided into two sections according to whether 

 there is present or not a sutural stria on the wing case. This grouping may be 

 thus tabulated : — 



Group 1. — Head with an even, distinct, raised front margin : in the other gi'oups 

 (except in Nos. 256 and 257) the head is without a definite margin. 



Species Nos. 242 and 243. 



Gkoup 2. — Thorax with a minute basal plica or impression, which is not in the 

 least continued on to the elytra ; apex of elytra very acuminate. 

 Species 244 to 246. 



* Besides these eighty species, the following descriptions may, (with the exception of the first of them), 

 be assigned with considerable certainty to the genus : — 



Hydrogly]ihus flaviculus, Motseh. (No. 1,335 huj. op.); Ceylon. — Hydroponis adumbratus, Clk. (No. 

 1,338), near No. 308 ; Mexico. — Hydroponis amandus, Lee. (No. 1,339), Group 5 B. ; North 

 America. — Hydroporus angularis, King. (No. 1,340) ; Nubia. — Hydroponis atomus, Eegt. (No. 

 1,342), ? near No. 307; Manilla.— Hydroponis charlotti, Clk. (No. 1,350), ?=No. 318; Mexico.— 

 Hydroporus elegantuliis, Boh. (No. 1,36G), 1 near^No. 252 ; Caffraria. — Hydroponis emiliauus, Clk. 

 (No. 1,3G7), ?=No. 318; Mexico. — Hydroponis evanescens. Boh. (No. 1,308); Caffraria. — Hydro- 

 ponis fryi, Clk. (No. 1,372),? near No. 256; Mexico. — Hydroporus intirmus. Boh. (No. 1,385), 

 near No. 269 ; Caffraria. — Hydroporus magensis, Clk. (No. 1,396) ; Mexico. — Hydroponis nico- 

 baricus, Redt. (No. 1,403) ; Nicobar Islands. — Hydroponis obscurus, Bab. (No. 1,407), ?=No. 313 ; 

 Brazil. — Hydroponis pseudo-geminus, Regt. (No. 1,420) ; Manilla. — Hydroponis seminulum, Lee. 

 (No. 1,431), 1 Group 2 ; North America. — Hydroporus subtUis, Lee. (No. 1,436), Group 5, B ; 

 North America. — Hydroporus tetragrammus, Hoch. (No. 1,441), near No. 270 ; Caucasus. 



