354 Illinois State Laboratory of Natural History. 



the forms preferring life amongst vegetation and near the 

 shores or bottom doubtless often mingled with those inhabit- 

 ing the clear open water, the same forms being usually found 

 in both surface and bottom towings. The amount of aquatic 

 vegetation present was an important item in the question. 

 In Phelps and Thompson's lakes and in the river at E there 

 was comparatively little visible plant life, while at D — in the 

 river — and in Quiver and Dogfish lakes aquatic plants of all 

 kinds flourished ; indeed, Quiver Lake was almost entirely 

 choked up during the first summer and autumn with Cerato- 

 phyllum, Elodea, Spirogyra, and the like. There was, how- 

 ever, a slight current in Quiver Lake, which kept a narrow 

 channel free from weeds, so that it was possible to take tow- 

 ings at C during the entire season. On the whole it seems 

 most satisfactory to consider those forms found near the 

 shore or among vegetation as littoral, and those taken in 

 open water free from vegetation as pelagic. Of the species 

 studied the following tw r enty-four are in this sense pelagic : 



Conochilus dossuarius Hudson. 



C. unicornis liousselet. 



Asplanchna ebbesbornii Hudson. 



A. brightwellii Gosse. 



A. priodonta Gosse. 



A. herrickii de Guerne. 

 Synchaeta pectinata Ehrbg. 

 S. stylata Wierz. 

 Polyarthra platyptera Ehrbg. 

 Triarthra terminalis Plate. 

 Plcesoma lynceus Ehrbg. 

 Brachionus mollis Hempel. 



B. pala Ehrbg. 

 B. dorcas Gosse. 



B. dorcas spinosus Wierz, 

 B. punctatus Hempel. 

 B. variabilis Hempel. 

 B. angularis Gosse. 

 B. angularis bidens Plate. 

 Anuria tecta Gosse. 



