108 University of California Publications in Zoology [ VoL - 



Discussion op Genera 

 Bosmina longirostris O. F. Mull. 



Station I Station II Station III Daily Hourly 



Average 746 5,000 5,145 1,652 13,684 



Identification probable. This form was rare at Station I, being 

 recorded only eleven times in small numbers, six times in September 

 and October, the rest scattering. Catches at the other stations were 

 almost confined to the same period but there were more of them and 

 the numbers were larger. Clearly favored by warm, stagnating water 

 and retarded by sewage. 



Chydorus sp. 



Station I Station II Station III Daily Hourly 



Average 1,662 1,555 



Identification doubtful. Recorded seven times at Station II mainly 

 in August and September, and five times at Station III at irregular 

 intervals. No definite conclusion possible, though the indication is 

 that sewage is injurious, while warm stagnating water is favorable. 



Sida sp. 



Station I Station II Station III Daily Hourly 



Average 2,960 738 1,325 5,781 21,068 



Identification doubtful. There was probably considerable confus- 

 ion with other forms, especially Daphnia. Recorded frequently at 

 Station I from early June to late October, rarely at other times. Num- 

 bers always small except on October 1 (105,792). Recorded twice at 

 Station II and seven times at Station III, nearly all in the warm 

 months. Seems to be a warm water form favored by sewage and quiet 

 waters. 



The following other genera of Cladocera were thought to be pres- 

 ent : 



Alona sp. 



Bosmina sp. All three stations. 



Daphnia sp. 



Ostracoda 

 Ostracoda were mainly notable for their absence. Cypris sp. was 

 the only form recognized and it was rare. It was not recorded from 

 the preserved material. Inasmuch as it has been found in abundance 

 in ditches and temporary ponds about Stockton, it must be regarded 

 as strictly adventitious. 



