NORTH AMERICAN COLEOPTERA. 237 



Notes ou some HYDROBIIBfl of Boreal America. 



BY GEO. H. HORN, M. D. 



The genera and species of this tribe, as far as they were then 

 know to nie, were made the subject of a study and the results pub- 

 lished in Proceedings Anier. Philos. Soc. 1873, pp. 118-137. The 

 basis of this work was furnished by the collection of Dr. LeConte, 

 together with my own, so that the species were represented in most 

 cases by fair series of specimens with very few uniques. Since that 

 time but three species have been described, although numerous col- 

 lections have been made, adding greatly to our series of those known. 



In the generic division, adoj^ted in the above-mentioned paper, a 

 very conservative course was followed, and only those genera which 

 had received the sanction of Lacordaire and the authors of the 

 " Catalogus" were recognized. Numerous subdivisions of Hydro- 

 bius and Philydrus had been proposed, notably by Mulsant and 

 Thomson, which were not viewed with much favor at the time of 

 my essay. In 1870 (Ent. Mo. Mag. p. 373), Dr. Sharp added to our 

 knowledge of some of these genera by amplifying the diagnoses and 

 illustrating them b}^ some well executed detail sketches drawn by 

 Mr. Rye, although he did not at the time seem to have a thorough 

 conviction of the validity of the greater number of them. 



In 1881, Mr. Bedel (Faune du Bassiu de la Seine) admits the 

 validity of Paracymus and Anacsena of Thomson, and Helochares 

 of Mulsant, at the same time suggesting two new genera : Crenitis, 

 separated from Hydrobius and Cymbiodyta from Philydrus. 



More recently Dr. Sharp has studied the species of the Central 

 American fauna (Biol. Cent. Am. 1, 2) with the result of adding 

 Metacymus, Sindolus, Chasmogenus and Hydrocombus, the first 

 being related to the small Hydrobius forms, the last three to Phily- 

 drus. He has not admitted any of the genera into which Hydro- 

 bius had been divided. 



The object of the present paper is to give the the results of a study 

 of the species in our fauna in their relation to the genera which have 

 been proposed by the various authors above cited and at the same 

 time it is hoped to define the species more sharply by the important 

 aid afforded by vastly increased material and the discovery in them 

 of sexual characters which have proven of great utility. 



