182 THE CANADIAN ENTOMOLOGIST. 



ee. Tarsi not compressed, metasternum not prolonged into a spine. 



g. Last ventral segment emarginate Berosus. 



gg. Last ventral not emarginate. 



h. First and second ventrals concealed by 



plates C/icetarthria. 



hh. Ventral segments uncovered. 



i. Antennae 8-jointed, colours mostly pale, form 



rounded, convex Laccobius. 



ii. Antennae 9-jointed, colours usually dark. 



j. Terminal joint of max. palpi shorter than pre- 

 ceding, 

 k. Tarsi 5-jointed on all the feet. 



Mesosternum with longitudinal 



lamina Philhydrus. 



Mesosternum with slight median 



tuberosity Helochares. 



kk. Tarsi 4-jointed on middle and hind feet. 



Mesosternum with feeble transverse carina, 



claws simple Cynibiodyta. 



Mesosternum with compressed conical pro- 

 cess, claws broadly toothed at 



base Helocombtis. 



jj. Terminal joint of max. palpi longer than the 

 preceding. 



Elytra striate or striato-punctate....i7y^;-<?^/W. 

 Elytral punctuation confused. . . . Crenephilus. 

 dd. Middle and hind tarsi with the first joint elongate. 

 1. Mesosternum narrow, prosternum carinate. 



Larger species ; scutel elongate Sphczriditim. 



Smaller species ; scutel equilateral Cercyon. 



11. Mesosternum very wide, prosternum with elevated flattened 

 median area. 



Prothorax margined Megastenium. 



Prothorax not margined Cryptopleurum. 



Helophorus, Fabr. 

 These insects are of a more or less elongate form and rough 

 sculpture ; they may be found in numbers by stirring up the bottom near ; 

 the banks of pools, when the beetles will float to the top of the water/ 



