Occasional Papers of the Museum of Zoology 17 



in small minihers in the larger beach pools which have a con- 

 siderable area free from emergent vegetation. Miss Miller 

 reported thirteen specimens from North Fishtail Bay (Sta. 

 l\'), on July 26, 1913, but no others were taken there either 

 in that year or in the other years. 



Except for five specimens taken at Station XII on July 5, 

 this species was never found in emergent vegetation or in shal- 

 low water. It was commonly seen floating at the surface of 

 open water, ready to dive at any time ; and it is the wariest 

 Xotonecta of my acquaintance. This was the only species of 

 the genus of which imagoes were found early in July at 

 Douglas Lake. 



15. Notonecta nndnlata Say. The most abundant and 

 widely distributed back-swimmer in the Douglas Lake region, 

 common in all the quiet-water habitats except Bessey Creek. 

 Like the last species, A^ undulaia was seldom found among 

 the vegetation in the larger pools, but was most often observed 

 floating at the surface in the open water, a few feet outside 

 the plant zone. Like most of the other species of the family, 

 iindulata was much more abundant in the later part of the 

 summer than earlv in July, imagoes being found only occasion- 

 ally before about July 20. 



About five percent of the specimens lacked the black fascia 

 at the apex of the corium, and in one specimen there was no 

 trace of black on the scutellum. 



16. Notonecta insiilata Kirby. One of the least common 

 species of the genus in this vicinity. No specimens were se- 

 cured either in 1913 or in 1914; and in 1918 only seven speci- 

 mens were taken, at Stations IX and XII. 



Genus Bukxo.v Kirkaldv 

 The various species of this genus with whicli 1 am acquaint- 

 ed in life a])iicar to liave a very nicely adjusted mechanism for 

 maintaining their position at any level in the water without 



