96 Vniverxitif of Californ'ui PuhVicntions in Zooluijn [Vol.22 



The numbers here were much hirger than those noted in Illinois 

 and the vernal maxima eame about a month earlier. Otln'i'wise there 

 is rather close similarity in the records. Recurrent pulses are not 

 distinct, however, at any of our stations here. 



Brach'uinus capsuliflonis I'ullits. (li. bukvri pjhrbg.) 



St:ition I Stiition II Station III Daily Hourly 



Average 1,9.54 14,418 9,5S2 1,44.5 40,468 



Identification probable. Occurrence at Station I scattered, in 

 small numbers, from May to December, with a small maximum in 

 October. Occurrence at Station II almost limited to August and Sep- 

 tember, with a maximum in September. At Station III somewhat sim- 

 ilar, except for a slightly larger number of earlier records of small 

 numbers. 



The likeness to Illinois conditions is very marked, especially at 

 Station II. Our records indicate that sewage is detrimental while 

 stagnation and rather high temperature (near 24° C.) are beneficial. 

 It seems rather strange that though the river showed the largest niun- 

 bers, the limits of their occurrence were much more sharply defined 

 than at the other stations; only four small catches being found out- 

 side of the eleven weeks period from August 2 to October 11, as against 

 twice that number elsewhere. No males were recognized. 



Brachioniis ijatidus Miill. (B. militaris Ehrbg.) 



Station I Station II Station III Daily Hourly 



Average 120 4,804 1,6:11 .'UO 10.469 



Identification certain. Recorded only once at Station I in July 

 (6,400). Occurrence at Stations II and III limited to July and 

 August and September, except for one catch on December 6 at Station 

 II. Maximum on September 6 at both places. Evidently a summer 

 form favored by stagnation but intolerant of sewage. No data are 

 at hand bearing upon Kofoid's suggestion (190tS) that this species 

 probably thrives in warm, shallow water rich in organic matter. Its 

 absence from sewage does not prove that it would be injured by 

 decaying vegetation, etc. 



Brachioniis plicatilis Miill. (B. miiUcri Ehrbg.) 



Station I Station II Station III Daily Hourly 



Average 9,179 977 96.5 41,3 



Identification usually satisfactory. Occurrence at Station I mainly 

 in first tliree months, thereafter in small numbers at variable but 

 usually wide intervals through the year. Maximum (132,240) twice, 



