344 On Aquatic Carniworous Coleoptera or Dytiscile. 
I. 22.— Genus BIDESSUS. 
Prosternal process longer than broad, parallel-sided, but with a more or less 
acute extremity which attains the metasternum ; intercoxal process of metasternum 
not attaining the mesosternal fork, so that when the prothorax is taken away it may 
be seen that the middle coxee touch one another ; posterior tibize with the basal 
portion much more slender than the apical one. Coxal 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 groups 
(except in Nos. 256 and 257) the head is without a definite margin. 
Species Nos. 242 and 243. 
Group 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 :— 
Hydroglyphus flaviculus, Motsch. (No. 1,335 huj. op.) ; Ceylon.—Hydroporus adumbratus, Clk. (No. 
1,338), near No. 308; Mexico.—Hydroporus amandus, Lec. (No. 1,339), Group 5 B.; North 
America.—Hydroporus angularis, Klug. (No. 1,340); Nubia.—Hydroporus atomus, Regt. (No. 
1,342), ? near No. 307 ; Manilla.—Hydroporus charlotti, Clk. (No. 1,350),’=No. 318; Mexico.— 
Hydroporus elegantulus, Boh. (No. 1,366), ? near,No. 252 ; Caffraria.—Hydroporus emilianus, Clk. 
(No. 1,367), ?=No. 318 ; Mexico.—Hydroporus evanescens, Boh. (No. 1,368) ; Caftraria.—Hydro- 
porus fryi, Clk. (No. 1,372),% near No. 256 ; Mexico.—Hydroporus infirmus, Boh. (No. 1,385), 
near No. 269 ; Caffraria—Hydroporus magensis, Clk. (No. 1,396) ; Mexico.—Hydroporus nico- 
baricus, Redt. (No. 1,403) ; Nicobar Islands.—Hydroporus obscurus, Bab. (No. 1,407), =No. 318 ; 
Brazil.—Hydroporus pseudo-geminus, Regt. (No. 1,420) ; Manilla——Hydroporus seminulum, Lec. 
(No. 1,431), ? Group 2; North America.—Hydroporus subtilis, Lec. (No. 1,436), Group 5, B; 
North America. 
Hydroporus tetragrammus, Hoch. (No. 1,441), near No. 270 ; Caucasus. 
