Horn.] 1^ [Feb. 21. 



punctures at the sides and apex of elytra somewhat coarser but not form- 

 ing rows. Length .14 inch ; 3.5 mm. 

 Occurs in the Western Canada region. 



P. rotundus, Say (Hydrophilus), Journ. Acad. V, p. 188; Lee. Proc. 

 Acad. 1855, p. 369 ; nitens, Zimm. Trans. Ent. Soc. 1809, p. 250. 



Broadly oval, convex, black, shining, sides of elytra feebly explanate 

 and piceous. Surface finely but not very densely punctured, punctures 

 of the elytra coarser and gradually evanescent toward the apex, at sides 

 with a few coarser punctures sparsely and irregularly placed. Body 

 beneath and legs black, mesosternum with a distinctly elevated trans- 

 verse line. 'Length .28 inch ; 7 mm. 



Resembles superficially P. ductus, but may be known by the smoother 

 surface and absence of any mesosternal crest. 

 Middle States and North Carolina. 



Hydrobius. Leach. 

 The species of this genus are more heterogeneous than those of Philliy- 

 drus, and a close resemblance may be noticed in superficial characters 

 between several species of the two genera which will be noticed in their 

 proper places. 



Notwithstanding the very odd appearance of Sperchopsis tesselatus, Lee. 

 I can find no character by which it maybe separated from Hydrobius. 

 The genus Paracymus, Thorns, appears to be merely a section,»as I find 

 the hind femora varying in punctuation in several of the species from the 

 type of Hydrobius leading directly to the form seen in Paracymus. 



Hydrobius may be known from Philhydrus by the fourth joint of the 

 maxillary palpi longer than the preceding and very nearly equal to the 

 second. In the section Paracymus the palpi are somewhat shorter and 

 stouter. 



The species may be divided in the following manner : 

 Hind femora densely punctured, pubescent and opaque at 



base Hydrobius. 



Hind femora sparsely punctured and glabrous Paracymus. 



The species of Hydrobius proper are, 



Prosternum carinate or acutely elevated at middle in 

 front. 

 Mesosternum simple ; elytral intervals unequally 

 convex. 

 Very convex, shining ; elytral intervals smooth. . tesselatus. 



Depressed, opaque ; elytral intervals scabrous. . . . scabrosus. 



Mesosternum prominent ; intervals flat. 



Surface feebly shining ; elytral intervals finely 



scabrous latus. 



Surface shining ; mesosternum strongly cristate ; 



intervals punctulate t" /aid us. 



Prosternum not carinate. 



Form globose ; elytra with rows of puncture globosus. 



Form oblong ; elytra more or less striate fuscipes. 



