262 GEO. H. HORN. 



The following is the definition of the genera recognized in our 

 fauna : 



Elytra either striate or striato-puiictate Hydrobius. 



Elytra with confused punctuation ; head, thorax and elytra, without the series 

 of coarse punctures C'reiiipliillis. 



Hydrobiiis has the middle and posterior tibia? fimbriate at apex 

 with short, nearly equal, closely set spinules, while in Creniphilus 

 the spinules are relatively long and irregular, not closely placed, 

 PI. iv, figs. 10-11. 



HYDROBIUfii Leach. 



Maxillary palpi with the terminal joint always longer than the 

 preceding. Prothorax either without or with basal marginal line, 

 in the latter case indistinct and visible only at the sides of base. 

 Elytra more or less deeply striate, or simply with striae of punctures, 

 interstices usually puuctulate or scabrous, and with the coarser series 

 of punctures on the alternate intervals beginning with the third, 

 except in scabrosus and tesseUatus. Femora more or less pubescent 

 beneath, sometimes but feebly near the base. Tibiae fimbriate at 

 apex with short, closely set spinules. Posterior tarsi slender, not as 

 long as the tibise. 



It will also be observed in three of the species that the head has 

 the coarser series of punctures forming an arcuate row as in the 

 Philydroid genera, and on the thorax also similar groups, although 

 liere they unite in a semicircular row convex to the side margin. 



The raesosternal protuberance does not have here the same im- 

 portance observed elsewhere, as it varies considerably within specific 

 limits, notably m fiisci])es. 



In the present essay the genus is limited to the large species with 

 the elytra striato-punctate, or striate in ten regular .series. Even as 

 thus restricted to a small number of species, it is more heterogeneous 

 in aspect than any other genus in the family. On characters which 

 are now admitted to be unimportant nearly every species in the Eu- 

 ropean fauna has at one time or another had a separate generic name 

 suggested for it. Our species would be in the same plight if similar 

 characters were made use of, with the result of unnecessarily com- 

 plicating the study. 



The following analytical table will enable the species to be sepa- 

 rated : 



