THE GENERA HYDROCHUS, OCTHEBIUS, AND HYDR.ENA. 163 



parallel elytra, each of which has six rows of large punctures 

 between the suture and the shoulder. Common, and generally 

 distributed in England and Scotland. 



b. Length, § line. Elytra with sides rounded and dilated 

 behind middle, sharply truncate at apex; thorax with light 

 margins. 



H. atricapilla, Wat.— The truncate elytra are alone sufficient 

 to separate this species at once from all others ; the regular 

 punctuation of the elytra (each of which has six rows of punctures) 

 is also a distinguishing mark. The palpi of the male are very 

 much thickened ; at first sight it bears a superficial resemblance 

 to H. pygmcea. Local. Scarborough, the Wansbeck (Northum- 

 berland), Ochil Hills (Scotland). It appears to be a northern 

 insect. 



B. Punctuation of elytra more or less feeble and irregular, 

 especially behind the middle ; thorax with light margins. 



H. pygmcea, Wat. — Thorax strongly punctured ; elytra with 

 six rows of punctures on each, between the suture and the 

 shoulder, fairly strong and regular at the base, but hard to 

 distinguish behind the middle ; thorax strongly contracted at 

 base ; elytra rounded at sides and apex. Male with femora 

 thickened, and tibiae dilated at base, but narrowed towards apex. 

 Length, f line. Rare. Scarborough, the Wansbeck (Northum- 

 berland). 



H. palchella, Germ. — Distinguished from the preceding by 

 its usually smaller size, more parallel shape, lighter colour, 

 duller appearance, and less strong punctuation of the thorax and 

 base of elytra, each of which has six rows of rather feeble punctures 

 between the suture and the shoulder, the outer ones being rather 

 confused ; the margins of the thorax are also more broadly 

 testaceous, and of lighter colour than in the preceding species. 

 Length, f line. Rare. Scarborough, Derbyshire, the Wansbeck. 



The Hydrcence are usually found in running water. H. palus- 

 tris, H. riparia, and II. testacea, however, and probably other 

 species, also occur in stagnant water. 



I am much indebted to Dr. Power and Mr. Champion for 

 hints as to localities, &c, for the species. 



The School House, Lincoln, June 5, 1884. 



