1921] Hussey — Distributional Notes on Tlemiptera 11 



southwestern part of the state, near Three Oaks (June to Sep- 

 tember). These were all taken from woodland pools, or from the 

 slow- flowing stretches of the G alien Eiver in dense woods. 



Gerris alacris, sp. no v. (Fig. 1). 



Facies of G. marginatus Say, a little smaller than that species, 

 females larger and more robust than the males; commonly brachyp- 

 terous. Males readily distinguished from the other North Amer- 

 ican species by the prominent omphalium of the metasternum; 

 female easily distinguished from G. marginatus by the shorter 

 spines of the sixth abdominal segment, which only slightly surpass 

 the middle of the first genital segment. 



Black above, the pronotum and the veins of the hemielytra with 

 fine sparse golden pubescence, anterior lobe of the pronotum with 

 a yellow inedian line, two small oblique yellowish marks on the 

 base of the vertex. Buccula3 yellow, throat slate-gray; prosternum 

 yellow, the coxal cavities with a black spot outside. Mesosternum 

 blackish, often yellow posteriorly, commonly with two diverging 

 yellow lines extending backward from between the anterior coxae. 

 Metasternum and venter yellowish, median line obsoletely carinate, 

 the sides of the abdomen below and the region about the metasternal 

 orifice (omphalium Bergroth 1902) blackish. The color of the 

 ventral surface is variable: sometimes it is entirely black. Con- 

 nexivum narrowly yellow ontside. 



Antennas dark testaceous, first and second joints with a narrow 

 piceous apical ring, middle of the first joint darker; apical half 

 of the third and the entire fourth joint piceous. Eelative lengths 

 of the segments, 43:21:20:30 (average of 15 specimens). These 

 ratios vary within narrow limits: sometimes the third segment 

 is very slightly longer than the second, and sometimes the first is 

 slightly shorter than the second and third together. 



Legs colored as in marginatus, the middle and hind legs slightly 

 longer than in that species. In the brachypterous form the hemi- 

 elytra commonly reach to about the middle of the third abdominal 

 segment. 



Male: sinus of the sixth ventral segment similar to that of 

 marginatus, but with the sides of the median emargination some- 

 what more parallel. Female: genital segment broad at the base, 



