150 



THE CANADIAN ENTOMOLOGIST. 



cc. Elytra hardly distinctly punctured, sometimes appearing very 



finely punctulate or partially aciculate. 



d. Middle thighs with long, conspicuous seta3 . . Ther?nonectes 



dd. Middle thighs with short, inconspicuous sttT^.Graphoderes. 



The emargination of the tips of the tibial spurs in the last three 



genera is very fine, and must be looked for with care, and a good lens. 



The other characters seem sufficiently evident if ordinary discrimination 



is used. 



Hydaticus, Leach. 



Three of these occur, which are distinguished with some difficulty, 

 excepting in the case of well-marked individuals, which separate thus : — 

 Above rufo-piceous, sides of thorax and of elytra obscurely rufo-testaceous, 



.50 in picetts, Lee. 



'Above piceous, thorax rufous with black basal fascia. Elytra with 



distinct yellow margin. 



Larger (.50 in.). Elytra with margin and usually a basal band from 



v/hich extend four or five longitudinal lines, fulvous. ..siagnalis, Fabr. 



Smaller (.48 in.). Elytra with a submarginal yellow vitta, recurved at 



the humerus and attenuated to the end, which is behind the middle, 



margin rufous towards the tip bimarginatus. Say. 



DvTiscus, Linn. 

 Eight species are on the Canadian lists, and are easily known from 

 all other Dytiscida?, except Cybister, by their large size. The sides of the 



thorax and usually the front and hind margins are 

 yellow, the outer margins of the elytra always so. 

 They separate into groups according to the form of 

 the labrum and of the hind coxal plates, the proc- 

 esses of which extend slightly over the apparent 

 bases of the hind legs, and are divergent and either 

 rounded, simply acuminate, or spinose at tip. The 

 females of some species have sulcate elytra, while 

 others are smooth. The spiracles of all make very 

 pretty objects for the microscope, being protected 

 by dendroid hairs which fringe the margins, and well 

 repay the trouble of preparation. In the following 

 table I have substituted the name circunicinctus, 

 Ahr., for auxins, Mann., following the opinion 

 doubtfully expressed in the Henshaw Check List, 



Fig. II. 



