THE WHERRYMEN OR WATER STRIDERS. 971 



the femora of hind ones much surpassing tip of abdomen. 

 Eleven species have been recorded from our territory. 



KEY TO EASTERN' SPECIES OF GERR1S. 



a. Joint 1 of antennae distinctly longer than 2 and 3 united; larger, 

 length 14 or more mm. 

 b. Pronotum without a median carina; under side of body dark; elytra 

 usually absent; spines of sixth ventral not reaching apex of 

 genital. 1106. remigis. 



bb. Hind lobe of pronotum with a distinct median carina; under side 

 of body usually yellowish or silvery-gray; elytra always present 

 though sometimes abbreviated ; spines of sixth ventral slightly 

 surpassing apex of genital. 

 c. Hind margin of sixth ventral of male broadly and shallowly con- 

 cave. 1107. CONFORMIS. 

 ex. Hind margin of sixth ventral of male deeply and roundly concave. 



1108. NEBULARIS. 



iki. Joint 1 of antennae not or but slightly longer than 2 and 3 united; 

 smaller, length usually less than 11 mm. 

 d. Antennae less than half the length of body, not extending beyond 

 the pronotum ; sixth ventral of male with hind margin usually 

 sinuate or doubly concave, its spines rather short and stout, at 

 most passing but little the middle of genital plate; under sur- 

 face usually blackish. 

 e. Side margins of front lobe of pronotum concolorous with the disk. 

 /'. First ventral genital segment of male without a tuft of long 

 hairs each side. 

 g. First joint of antennae only about one-sixth longer than fourth; 

 spines of sixth ventral of female reaching to or beyond middle 

 of genital plate. 

 h. Male with median notch of hind margin of last ventral nar- 

 rowly rounded (fig. 194, b) ; first genital less convex and 

 with a median keel. 1109. marginatus. 



hh. Male with median notch of last ventral deeply and roundly 

 notched ; first genital very convex and without a keel. 



1110. INSPERATUS. 



gg. First antennal one-fourth or more longer than fourth ; spines 

 of sixth ventral short, obtuse, not reaching middle of genital 

 plate; abdomen in great part usually dull yellow. 



1111. ALACRIS. 

 //. First ventral genital of male with sides deeply depressed and with 

 a tuft of long hairs in each depression. 1112. comatus. 



ee. Side margins of front lobe of pronotum with a pale stripe. 



i. Bases of elytra wholly dark; second or median emargination of 

 sixth ventral of male broadly rectangular (fig. 194, c) . 



1113. BUENOI. 



it. Inner basal margins of elytra marked with yellowish-white lines 



between the veins; median emargination of sixth ventral of 



male semicircular (fig. 194, «). 1114. argenticollis. 



