872 On Aquatie Carniworous Coleoptera or Dytiscide. 
most extensive genus of the Dytiscide. The insects are always of small size (2-6 
in.m. in length), and show much variation in colour, punctuation, pubescence and 
outline, but are distinguished from all the other Hydroporini by the fact that the 
mesosternal fork is connected with the intercoxal process of the metasternum. The 
head is never margined in front ; the epipleurse are always slender, and there 1s never 
any definite genicular fossa at the shoulder ; the prosternal process varies a good 
deal, but is uever truncate behind. There is no ligula on the inner face of the 
elytra ; the swimming legs are always feeble, and their femora are never thick, and 
their postero-external angle is rounded or obtuse: their tarsi are slender and 
feeble, and the joints are not co-adapted to one another so as to give rigidity ; they 
are terminated by two small, slender, equal claws: the posterior coxal cavities are 
quite approximate, or at any rate very nearly so, and the hind coxa is not very 
large, so that it is largely separated by the metasternum from the middle coxal 
cavity. The scutellum is quite concealed. The front and middle tarsi have only 
four visible joints. The distinctive characters of the sexes are slight, and sometimes 
external differences can scarcely be found. In a few species dimorphic females 
occur. 
In distinguishing the species of Hydroporus, great importance has been attached 
by describers to the continuity or discontinuity of the outline of the body at the 
point of the junction of the thorax and elytra. This character is of real importance, 
for it is correlative with important structural changes in the mesosternum ; when 
this part is larger, or takes a less completely vertical direction than usual, then 
the outline of the body is much interrupted at the point of junction of the thorax 
and elytra ; with this there is frequently associated an elongation of the prosternal 
process. 
The continuity of outline depends also largely on the extent to which the humeral 
angle of the wing-case is developed, and extended into a covering for the knee ; 
comp. on these points Dytiscus palustris, (No. 612) Hydroporus modestus, (No. 
627) and Hydroporus melanarius, (No. 555). 
The genus is especially characteristic of the northern portion of the two hemi- 
spheres, with a few species in parts adjacent thereto, as in Mexico, Guatemala, 
Persia &c.; but there is also a species in South Africa and two in southern South 
America (Chili and Monte Video). A considerable number of additional species 
will no doubt be discovered in the northern portions of the New World. ‘The 
absence of the genus from Japan is a fact well worthy of notice. 
I, 42.—Genus CHLINA. (Vide p. 487.) 
Six species form this aggregate. They are insects of small size, (4-6 m.m. in 
iength), of narrow, parallel form, but little convex beneath, of uniform, obscure 
colour, destitute of pubescence, and with mucronate termination of the body. Ihe 
