838 On Aquatic Carnivorous Coleoptera or Dytiscide. 
very little developed, and quite feeble, the hind margin of their femur bears some 
very elongate set at the apex, the tarsi are rather shorter than the tibie, and their 
basal joint is longer than the three following ones together. 
This insect is peculiar to North America. 
It is an interesting example of very different stages of evolution of portions of 
one organism; the very feeble and low organization of its swimming legs contrast 
very forcibly with the extremely high differentiation of the anterior legs. It is 
probably a very imactive creature: and apparently rare, as I have not been able to 
obtain a specimen for dissection. 
L. 8.—Genus SUPHIS. (Vide p. 268.) 
Three species is all that at present is known to constitute this aggregate; their 
individuals are of very peculiar form, being extremely convex above, and of very 
short oval form, attenuate and acuminate behind; the general colour is obscure 
yellowish, with the elytra darker and obscurely spotted ; the upper surface is closely 
punctured, and on the undersurface the breast is coarsely sculptured. The antennze 
are rather long and slender, the apical joints subserrate internally. The prosternal 
process is broad, truncate, or very nearly so, behind, and is continued forwards 
between the coxe, but is somewhat gradually flexed towards the front, so that it 
only presents in front a very small vertical face; the large anterior coxz are globose, 
and extend nearly to the front of the thorax, which presents only an extremely small 
band in front of them; the metasternum is separated from the hind coxa by a suture 
which departs but little from a straight transverse line: the coxal processes are 
very broad, nearly parallel sided, and are nearly truncate behind, the coxal cavities 
are separated by a rather broad space, which is marked off on each side by a broad, 
rather distinct, coxal notch. The front legs, and the other characters are much the 
same as in Colpius. 
The genus is restricted to the tropical parts of the New World. 
2 
I. 9—Genus CANTHYDRUS. (Vide p. 269.) 
This aggregate consists of about forty species ; they are small insects attaining 
only about 3 m.m in length, they are short in form, very convex above, much 
acuminate behind, frequently variegate in the colour of the upper surface, and this 
may be either very polished and free from sculpture, or on the contrary coarsely 
punctured. The antenne are very short, slender, frequently with one or more of 
the intermediate joints a little larger than the others. The last joint of the labial 
palpus is greatly dilated and obscurely notched or emarginate; the prosternal 
process is rather large and a little longer than broad, it is nearly truncate behind, 
the angles being nearly rectangular, the front coxee are not greatly separated from 
one another, and there is a moderately long anterior band of the prosternum ; the 
