12 



Psyche 



[February 



more narrowed apically than in marginatus; the spines of the 

 sixth ventral segment rather blunt; barely surpassing the middle 

 of the genital segment. 



Length, $, 7-8 mm., 2, 9-10 mm.; greatest width (across the 

 middle coxfe), 5 ^ 2.1-2.3 mm., 5 , 2.7-2.9 mm. 



Holotype, macropterous S , allotype, machopterous $ ,, in coll. 

 Museuni of Zoology, University of Michigan. Paratypes, 12 5 5 

 and 18 $ 2 , macropterous and brachypterous, in coll. University 

 of Michigan Museum and E. F. Hussey. 



Described from 32 specimens taken from a small pond at the 

 foot of a sand dune on the shore of Lake Michigan near Sawyer, 



Fig. 1. 1. Thorax of Gerrls alacris, n. sp., from left side. 2. Thorax of G. 



marginatus Say. 3. Gerris alacris, sp. nov., female genital segments, ventral 



aspect. 4. G. marginatus Say, female genital segments. 



Berrien County, Mich., July 19 and July 26, 1920 (E. F. Hussey). 

 This species was by far the most common water-strider here, and 

 Joth adults and nymphs were seen. In company with it were 

 G. marginatus and a few specimens of G. rufoscutellahis. 



Tenagogonus hesione Kirkaldy. One adult and three nymphs 

 of this water-strider were secured by Miss E. P. Butler at Vicks- 

 burg, Kalamazoo County, Michigan, August 21, 1920. The pre- 

 vious North American records were from Florida and Ohio. 



Microvelia circumcincta Champion. The LTniversity of Michigan 



