12 University of AlicJiigan 



occasionally found in company with G. rcmigis on the streams, 

 it appeared to prefer more slowly moving water than did that 

 species. 



The Dotiglas Lake specimens of Gerris riifosciiteUatiis vary 

 somewhat in the coloration of the hemelytra, which in the 

 majority of the individuals are concolorous. In two specimens 

 the ground color is white, with only the nervures rufous, and 

 other specimens show intergradation hetween this pattern and 

 the typical coloration. 



Genus Rheumatobates Bergroth 



6. Rlicmiiatobatcs rilcyi Bergroth. This little water-strid- 

 er was found in great numbers on Bessey Creek, where on 

 August 14, 1918, over one hundred adults were collected with 

 three sweeps of a net. In the same locality, on July 25, about 

 half a dozen nymphs of a later instar were taken on the 

 sheltered cove in North Fishtail Bay (Sta. IV). 



The adult specimens from Douglas Lake differ markedly in 

 color from Ohio specimens of typical rileyi in my collection, 

 and may possibly merit separation as a distinct variety. The 

 connexivum and disk of the mesonotum are entirely black in 

 the northern form, and the yellow marking of the pronotum of 

 typical rileyi is here reduced to narrow marginal lines on the 

 front and back edges connected by a moderately broad median 

 line. Only a narrow portion at the base of the first antennal 

 segment is yellow, and the yellow color on the coxae and tro- 

 chantera of the typical form is here replaced by reddish- 

 ochreaceous. There is a small yellow or orange spot on each 

 side of the mesothorax, just above the coxae. The mesonotum 

 is yellow, with a brown transverse band across the anterior 

 edge from which two obsolescent brown bands extended back- 

 ward, diverging posteriori}-, but not reaching the metasternal 



