838 On Aquatic Carnivorous Coleoptera or Dytiscidce. 



very little developed, and quite feeble, the hind margin of their femur bears some 

 very elongate setae at the apex, the tarsi are rather shorter than the tibiae, 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 inactive creature : and apparently rare, as 1 have not been able to 

 obtain a specimen for dissection. 



I. 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 antennae 

 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 coxae, but is somewhat gradually flexed towards the front, so that it 

 only presents in front a very small vertical face ; the large anterior coxae 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. 



I. 9.— Genus CANTH YDR US. ( 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 antennae 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 coxae are not greatly separated from 

 one another, and there is a moderately long anterior band of the prosternum ; the 



