108 INSECTS AT HOME. 



is called Elmis ceneus. One of these Beetles is shown on 

 Woodcut XII. Fig. 2, and the antenna is drawn at Fig. b of 

 the same illustration. 



All the species belonging to this genus, of which five British 

 examples are known, are very curious insects. They are plen- 

 tiful and yet are seldom found, and, indeed, are hardly ever 

 found except by those who know where to look for them. In 

 the first place, they are small, and would escape observation, 

 and in the next they are subaquatic in their habits, not swim- 

 ming about conspicuously like the Hydradephaga, but clinging 

 to the under side of submerged stones in swiftly-running 

 streams. Most aquatic Beetles prefer still water, but the 

 stream can never be too swift for the Elmis Beetles, which 

 will even select a waterfall as their place of residence. 



The present species is the commonest of the genus. 



As may be inferred from its specific name, the surface of 

 the insect has a brassy gloss. The thorax is squared, very 

 convex, and on either side of the disc is an elevated straight 

 line. The elytra are striated and punctured, and the under 

 surface of the body is clothed with thick golden down. Besides 

 the characteristics already given, the last joint of the tarsi is 

 very long, and armed with two large, sharp, and curved claws, 

 by means of which they are enabled to retain their position on 

 the stones in spite of the rushing water. It is rather remark- 

 able that, although the upper surface of the body is very 

 smooth, and the Beetles pass the greater part of their time 

 submerged in rapid streams, the body is often so caked with 

 mud that the shape of the insect is nearly obscured. 



Now we come to a very familiar but little imderstood 

 insect, popularly called the Black Water Beetle. Like some 

 of the preceding species, it has been confounded with the 

 Hydradephaga, merely because it inhabits the water, no re- 

 ference being made to its structure, or even its mode of 

 feeding. Indeed, I believe that scarcely any, except entomo- 

 logists, have the least idea that the Dyticus and the present 

 Beetle are not the same insect, the only ditFerence being that 

 one is much larger than the other. Now, if we examine this 

 Beetle, Hydrous piceus^ we shall find a vast number of struo 

 tural differences, as well as complete divergence in habits. 



