On Aquatic Carnivorous Coleoptera or Dytiscide. 861 
I. 34.—Genus HHROPHYDRUS,. (Vide p. 392.) 
Six species form this aggregate ; the individuals are of large size (comparatively 
with many other Hydroporides), from 4 to 6 m.m. of length: they are oblong- 
oval in form, very convex beneath; without pubescence, coarsely punctate; the 
head is either margined in front, with the margin interrupted in the middle, or is 
without margin ; the fourth joint of the front tarsus is but little elongate in com- 
parison with the others, which are narrow in proportion to their length, the third 
joint only obscurely bilobed, and the insertion of the fourth joint is nearer to the 
apical than to the basal edge of the third joint ; the front tibize are short, and 
rather broad ; the ridge on the inner face of the elytra is largely developed, rising 
gradually from the front towards the extremity till its greatest prominence is 
attained, and then falling abruptly, so that as regards one of its sides (the posterior) 
it forms a ligula, but as regards the other does not: the genicular area of the 
epipleurze is limited externally by a well-marked line ; the hind legs are slender; 
their coxee formed as in Ceelambus. 
The genus is nearly allied to Coelambus, but differs by the elytral ridge, as well 
as by the shorter, and comparatively broad, front tibize ; the shape of the tibiz 
suggests an approximation to Hydrovatus, which is confirmed by the rather small 
front tarsi, as well as by the swimming legs, slender and ill-developed in proportion 
to the weight and size of the insect. 
Madagascar is the metropolis of the aggregate, three species being peculiar to 
that island, while the other three are found in neighbouring regions,—two in South 
Africa, these two the most Coelambus like— ; while the sixth species has an exten- 
sive range, being found in Arabia, Senegal, Egypt and North Africa, and Southern 
Europe. 
I. 35.—Genus CHLAMBUS. (Vide p. 394.) 
This is an extensive aggregate, consisting of about fifty species; the individuals 
are convex beneath, but in other respects somewhat variable in form, usually 
oblong-oval, but sometimes shorter, even rotund in form ; they are nearly or entirely 
destitute of pubescence, the upper surface is usually pale, with distinct black marks, 
the under surface nearly always with coarse, (or moderately coarse) punctuation. 
There is always a distinct, and abrupt ligula on the inner face of the elytra, and 
the genicular area of the epipleura is well defined, and generally limited externally 
by a more or less raised line: the epipleuree are greatly reduced in breadth in their 
posterior portion, in fact opposite the hind margin of the second ventral segment 
there exists nothing of the epipleura but its two marginal lines, which have become 
contiguous. The front border of the hind cox has much extension in the anterior 
direction, (especially in the elongate species constituting the greater part of the 
genus), and the culmen or summit of its arch is narrow, and in extreme cases 
5828 
