906 On Aquatic Carnivorous Coleoptera or Dytiscidce. 



is almost withdrawn from articulation with the mesosternum.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 

 I am aware. 



The species are characteristic of the northern pai-ts of the Old and New Worlds, 

 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 antennae 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 cox?e are 

 rather large, and of the same shape as they are in Hydaticus, but their anterior 

 border is Avidely separated from the middle coxje. 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 iiTegular 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 Hydaticus, 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 especiallj- 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 hind angle of the 

 prothorax is obtuse and rounded. In these respects and some other details tho- 



