THK CANADIAN ENTOMOLOGIST. 



185 



T.ess elongate, more convex, abdomen pubescent, the last three 

 segments narrowly smooth at middle, without yellow spots at 



sides (1.25 in.) ovattis, G. & H. 



More elongate, less convex, first abdominal seg- 

 ment pubescent, the remainder broadly smooth 

 •M«s ^ at middle, and pubescent only at sides, which 



W^ are ornamented with large triangular yellow 



Viillilffl'l ^ spots (1.30-1.45 in.), (fig. IT,). triatigularis, ^3iY. 



iliiii V Tropisternus, Sol. 



liifB^^^^i^^^^^^^^ M ^^^^ three species on the Canadian lists are very 

 mI8 1^^^^^^^ I smooth, shining insects, mostly black above, and 

 ■.■illlllH^ ^ ofien extremely common in ponds. They are 

 among the best swimmers of the family. 

 Sides of thorax and elytra yellow 



(.33 in.) nimbatjts, Say. 



F"-- '3- Entirely black above. 



Surface finely and equally punctured (.40 in.) glaber, Hbst. 



Surface unequally and more coarsely punctured (.35 \\\.)mixtusX.^c. 

 Hydrocharis, Latr. 

 H:. obtusaius, Say, represents this genus. It is easily recognized by 

 the size (.60 in.), and by the elytra being so obtuse behind that the 

 posterior portion of the body is more blunt than the anterior. 



Berosus, Leach. 

 Very convex, rather elongate beetles of pale colours, with darker 

 maculitions in the form of thoracic and elytral spots. Quite possibly the 

 record oi ififuscatus msiy be incorrect. 



Abdomen cristate in $ , the fifth segment with one tooth at 



middle (.16 in.) peregrinus, Hbst. 



Abdomen never cristate, fifth segment bidentate at middle. 

 Elytral striae nearly obliterated on disk (.20-24 



in.) in/uscatiis, Lee. 



Elytral striae distinct and punctured on disk (.16- 



.20 in.) striatus, Say. 



Ch^tarthria, Steph. 

 Two very small convex species, .05 or .06 in. long, are representa- 

 tives of this genus. They occur on the margins of streams and ponds, 

 and separate easily thus : — 



Black above nigrella, Lee. 



Thorax more or less piceous, elytra testaceous pallida., Lee. 



