8 NORTH AMERICAN 



For purposes of measurement, the head is supposed to be limited by two sets 

 of tangent lines drawn to the eyes, one set parallel to the axis of the insect, 

 the other perpendicular to the same. 



The lines of juncture of the eyes with the interocular surface, called ocular 

 luns, are generally nearly straight, and have various degrees of convergence 

 in the different species. This is indicated by the number of head-lengths, 

 the poin of junction of these lines if produced, would be distant from the 

 anterior margin of the labrum. 



The numbers placed after the various localities indicate the number of 

 specimens from each, respectively. 



The o-enera and subgenera within our faunal limits may be tabu- 

 lated as follows : — 



Paraglossae not constricted at base ; genae of head large Dianous. 



Paraglossae strongly constricted at base ; genae generally absent, sometimes 

 visible from above, though very small. 

 Fourth tarsal joint simple or but slightly enlarged, not having well-defined 

 elongated lobes. 



Last joint of antennae longer than the penultimate StemiS. 



Last joint of antennae short, in the males much shorter than the penul- 

 timate Sub-gen. Mutinus. 



Fourth tarsal joint distinctly bilobed AreilS> 



DIANOUS Samouelle. 



In this genus there are two distinct types, viz.: copnrfrsceits Gyll, 

 and nitidulus Lee., to each of which there may be considered as 

 belonging two species, closely allied, it is true, but still distinct as 

 far as can be judged from the material at hand. In appearance the 

 species are robust, of a dark steel-blue color, having on each elytron 

 a large reddish-flavate spot. The eyes are much smaller than in 

 Stenus, and leave a large portion of the head exposed behind them ; 

 the distance between the eyes is much greater than in any of the other 

 genera of the group in our fauna. The antennae are very long and 

 slender, and the abdomen very strongly margined at the sides. Our 

 species, three in number, may be tabulated as follows : — 



Fourth and fifth joints of antennae equal in length or extremely nearly so. 

 Punctuation very sparse ; elytra scarcely longer than wide. 



1. nitidulus. 

 Punctuation very dense and fine ; elytra distinctly longer than wide. 



2. < Esah hens. 

 Fourth joint of antennae distinctly longer than the fifth; punctuation of 

 elytra sparse, strong ; elytra distinctly longer than wide. 



3. zepliyrus. 



