906 On Aquatic Carnivorous Coleoptera or Dytiscida. 
is almost withdrawn from articulation with the mesosternum. This species is 
frequently found in fish ponds and is said to cause much destruction amongst the 
fish ; whether the abundant supply of food the species procures has any connection 
with the great expansion referred to is a question worthy of consideration. 
The spinose coxal proceses found in certain species (e.g., D. circumflexus) is a — 
very interesting development; which is not found in any other Coleoptera so far as 
T am aware. 
The species are characteristic of the northern parts of the Old and New Worids, 
one is found as far south as Mexico, and in Persia; a species or two also occur in 
Japan, but not in the southern part thereof. 
I. 67—Genus PRODATICUS. (Vide p. 648.) 
The single peculiar species, has somewhat the form of a very large Agabus, but 
the elytra are variegated with large yellow marks in the style of the genus 
Sandracottus and its allies. The head is broad, the eyes are large and very convex, 
the antennee only moderately slender. The prothorax is without lateral margin, but 
its upper surface is flattened out or as it were expanded at the sides. The prosternal 
process is formed as in Hydaticus, but is rather narrower. The hind coxze are 
rather large, and of the same shape as they are in Hydaticus, but their anterior 
border is widely separated from the middle coxze. The coxal lines are fine and 
obsolete, but can nevertheless be detected ; they are greatly sinuate, being much 
approximated to the common suture at the axilla, and then greatly turned outwards 
so that the coxal lobes are broad; the supra-articular border marked off by them is 
indefinite and placed at the anterior part of the coxal lobe, quite as much as at its 
side, it is not very broad, there is a small coxal notch. The hind legs are rather 
stout and well developed for swimming, and their tarsi are terminated by two long 
claws of nearly equal length. 
The hinder tibia shows on its upper face an irregular series of punctures, about 
half the length of the tibia, and nearly parallel with its outer or upper border, the 
basal punctures are however nearer the middle of the face of the tibia than the 
outer ones are: the hind femora shows a group of obscure setigerous punctures, 
placed quite at its extremity but not at its hinder angle. 
Although this species has to a great degree the structure of Eaton; it departs 
therefrom in several important respects, the coxal lines are greatly turned outwards 
in their hinder portion, so that the coxal lobes and supra-articular border are of a 
different shape from what exists in Hydaticus, the coxal border especially is 
reduced in size and becomes less distinct ; the anterior border of the hind coxa is 
less arched, and consequently this piece is less in area than it is in any Hydaticus; 
the claws of the hind tarsi are of nearly equal length, and the bind angle of the 
prothorax is obtuse and rounded. In these respects and some other details the 
