On Aquatic Carnivorous Coleoptera or Dytiscide. 897 
borders of the coxe; on reaching the coxal process they are rather gently directed 
outwards, and leave the coxal lobe large and broad with a narrow supra-articular 
border ; the separation behind of the two coxal lobes is but slight, and they show 
only the very slightest trace of a coxal notch. The hind legs are rather powerful 
and well developed, the femora have a well marked lamina at the apex, with a 
sharply defined rectangular angle, and no trace of setze : their tarsi have the lower 
portions of the hind margins strongly lobed externally, and are terminated by two 
nearly straight closely applied claws, that are about equal to one another in length 
but the inner one is considerably stouter than the other. The apices of the elytra 
are slightly obliquely truncate. 
The position of the genus is decided in a positive manner by Rhantus marginatus 
in Lancetes (No. 917, Coptotomus argentinus, Reiche) ; although clearly allied to 
Coptotomus, this however differs strikingly from it in the form of the coxal lobes; 
these in Coptotomus are similar to what exists in Ilybius, whereas in the 
genus Lancetes the approximation in structure of the coxal lobes is to the very 
different form found in Dytiscus. The peculiar form of the prosternum is not so 
different to that of Lancetes, but may be defined as an exaggeration of the Lancetes 
prosternum after the manner of Cybister. 
The species are, so far as yet known, confined to the United States of North 
America. . 
I. 60.—Genus LANCETES. (Vide p. 602.) 
The five species associated to form this aggregate, consist of insects of rather 
large size for the Agabini (about 10 m.m. or over in length), they are of move or 
less narrow form, and their colour is a variegate mixture of black and yellow, or 
yellowish red, and they have very little sculpture; their appearance is greatly 
that of the species of Rhantus. The elytra are distinctly sinuate-truncate at the 
extremity, the coxal lobes elongate, and deeply separated from one another. The 
colour is a variegate mixture of black and yellow, or yellowish red, and they have 
very little sculpture. The prothorax is margined at the sides; the palpi have the 
apical joint only slightly or not at all incrassate, and with faint indications of an 
apical notch : the prosternum is thickened along the middle, but is not vertical in 
front ; the prosternal process is elongate and acuminate and received into a well 
developed cavity on the inter-coxal process of the metasternum. The hind coxze 
are moderately large, but the side wings of the metasternum are also large, and 
not deflexed outside the coxee. The coxal processes are very peculiar, the coxal 
lines are not greatly turned outwards to form the coxal lobes, and at the same 
time the separation between the two lobes is deep and elongate, so that the pro- 
cesses have a greater extension in the longitudinal direction, and a less in the 
transverse one than is usual, and the base of the articulation of the legs is more 
imperfectly covered and protected ; in all the species (except Colymbetes nigriceps) 
