llydrochlna.] nYDUOi'iiiLin.!:. 241 



the old genus IMiicocerii-^ Steph., shoulil be separated from OcUtelms, 

 and I find that M. Bedel is of tlie same opinion : the jjeculiar formation 

 of the palpi seems to afford a good generic character, 



I. Maxillary palpi with their last joint at. least as long 



as the pri'fcding. 



1. Maxilhii'j' palpi much shorter than head and thorax; 



eyes very prominent Hydeochus, Leach. 



2. Maxillary palpi at least as long as head and thorax j 



eyes not prominent Hyde^NA, Kuff. 



I I . Maxillary palpi with their last joint subulate, shorter 

 than the j)reeeding. 



1. Last joint of maxillary palpi very short, penulti- 

 mate much dilated IIexicoceeus, iS/f?/?/*. 



2. Last joint of maxillary palpi half as long as the 

 preceding, penultimate joint oblong, contracted 



in front OCTHEBIUS, Leach. 



HVDXIOCZ-IVS, Leach. 



This genus comprises about tliirty species, chiefly from Europe and 

 North America; species, however, occur also in Asia (Siberia, India, 

 and Ceylon), Northern Africa, and Oceania ; the genus is also repre- 

 sented in South America ; they are easily distinguished from the other 

 llydropliilidse by their projecting eyes, and the very. strong punctuation 

 of the elytra, of which tlie alternate interstices are often raised ; the 

 under side is clothed with a silky pubescence ; the upper side is some- 

 times l)lack, but more often metallic and iridescent; the species are 

 very poor swimmers, and their movements are exceedingly sluggish ; 

 they are found attached to plants in stagnant or slowly moving water. 

 Four out of nine or ten European species are found in liiiiain. 



L Form short and thick j elytra broad oval, much widened 



behind middle IL buevis, Ucrbst. 



II. Form elongate; elytra oblong or long oval, not much 



, widened behind middle. 



i. 3rd and oih interstices of elytra raised in ridges. 



1. Ridges of 3rd and 5th interstices efiaced behind ; 



length 3-t mm H. elongatus, Schall. 



2. Ridijes of 3rd and 5th interstices not effaced behind ; 



leLgth 2\-3 mm H. caetnatus. Germ. 



ii. ICIytra without any interstices raised in ridges . . H. angustatus, Germ. 



H. brevis^ Ilerbst. lUack or metallic lilack, rather shining ; head 

 and thorax thickly and coarsely punctured, the latter scarcely longer than 

 liroad, sinuate before posterior angles, with seven irregular depressions, 

 not very plainly marked as a rule, arranged in two transverse rows, three 

 in front and four behind ; elytra short, oval, much broader than thorax, 

 considerably widened behind middle, an<l thence narrowed to apex, with 

 very strongly punctured, crenate striae, alternate interstices raised ; 

 undersitle pubescent, silky black ; legs rather slender, pitcliy, or reddish 

 black. L. 2^-3 mm. 



Hare; Hovetou, Uoruing Fen, Woodbastwick (Dr. Power); Ouuiley, iVfarket 



ii 



