THE GENERA HYDROCHUS, OCTHEBIUS, AND HYDR^NA. 157 



gives Whittlesea Mere and Norfolk as localities. Of late years 

 it has occurred at Horning, Gumley (near Market Harborough), 

 Perth, Dumfries, and in the North of England. 



H. carinatus, Germ. — This species may best be described as 

 a diminutive H. elongatus, which it very closely resembles, 

 except that it is half the size of that insect. It was first taken in 

 Britain in 1859, by Mr. Dossetor, at Holme Fen, Huntingdon- 

 shire ; and has since been found in Wicken Fen, and other fen 

 localities. 



H. elongatus, Schall. — From the preceding insect this may be 

 distinguished by its duller appearance and much larger size. 

 From II. angustatus this and the two preceding species may be 

 at once separated by having several of the interstices of the elytra 

 raised into a carina or keel. Deal, Wicken and Burwell Fens, 

 Askham Bog, and many other localities. 



H. angustatus, Germ. — The interstices of the elytra of this 

 species are not raised, so that they present a flat evenly 

 punctured surface ; the depressions on the thorax are less 

 strong ; and the whole insect has a more shining iridescent 

 appearance. Generally distributed, but local ; commoner in the 

 South of England than in the North ; London district, New 

 Forest, &c. 



Of the Octhebii we possess nearly half the European species. 

 They are usually considered a difficult group, and it is certainly 

 hard to distinguish many of them without types, as the chief 

 distinctions lie in the impressions and furrows of the thorax ; and 

 it is hard to describe these, so that they may easily be recognised. 



Some writers divide the Octliebii into three groups: — 1st, the 

 species that have the elytra with strong punctured striae, com- 

 prising the first eight species of our catalogues ; 2ndly, those 

 that have the elytra with feeble punctured striae, contain- 

 ing 0. ceneus and 0. ceratus ; 3rdly, those that have the 

 elytra confusedly punctured, comprising the single species 

 0. punctatus. The punctuation of the first eight species, 

 however, differs so much inter se, that I have found from 

 experience that this distinction is of little practical value : 

 0. marinus, for instance, is very feebly striated when compared 

 with 0. exsculptus, although strongly striated when compared 

 with 0. ceratus. A better division for practical purposes might, 

 perhaps, be made by separating off 0. exsculptus, which used to 



