THE GENEBA H1DR0CHUS, 0CTHEB1US, AND HYDK^ENA. 161 



thorax, and in having the posterior angles of the thorax excised, 

 and filled with membrane. It is, however, abundantly distin- 

 guished from all our other species by its size, long white 

 pubescence, and by the fact that it is the only species of 

 the genus that has the elytra confusedly punctured. Very local. 

 I have found it at Lymington Salterns, where Mr. Champion has 

 also taken it; Dr. Power has found it at Worthing and Sheerness. 

 It appears to be a southern insect. 



Although the difference in size, as given, may appear to 

 be in some cases inconsiderable, yet it will be found that in 

 almost every case it will be possible to separate the insects 

 out into their divisions, even without the aid of a lens. So 

 far as my experience goes it would be almost impossible 

 to confound them, except in the case, mentioned above, of 

 a large 0. margipallens and a small 0. ceratus ; the former 

 being the largest species of the first group, and the latter 

 the smallest species of the second group. In case any difficulty 

 should arise with abnormal specimens, a glance at the sculpture 

 of the thorax will at once settle the matter. 



The genus Hydrcena is represented in the British list by nine 

 species (out of twenty -two given in the European catalogues). 

 They are chiefly distinguished by their general shape and size, 

 and to some extent by their colour ; and also by the number of 

 rows of punctures between the suture of the elytra and the 

 humeral angle, and by the shape of these punctures, which 

 in some species are round, in others more or less square. The 

 genus is distinguished from all the other Hydrophilidse by the 

 great length of the maxillary palpi, which are three times as long 

 as the antennas. 



I. Each elytron with more than six rows of punctures 

 between the suture and the humeral angle. 



A. Thorax testaceous, with disc at most darker. 



H. testacea, Curt. — Head black, thorax and elytra testaceous ; 

 metasternum with three raised lines, which are wanting in all the 

 other species ; thorax quite as long as broad ; each elytron with 

 eight rows of very strong punctures between the suture and the 

 humeral angle. Length, I line. Local; found in both stagnant 

 and running water. Notting Hill, Holm Bush, Epping, New 

 Forest, Lee, Wicken Fen, Loughton, &c. 



B. Thorax dark, with extreme margins only yellow. 



ENTOM. — JULY, 1884. Y 



