1920] Allen: Plankton of the San Joaquin River 53 



Fragillaria capucina Desm. 



Station I Station II Station III Daily Hourly 



Average 1,154 26,252 25,563 9,123 



Identification satisfactory. Colonies usually rather large, seldom 



less than six cells. Most of the colonies probably retained, though loss 



of small colonies and single cells may have been heavy. Numbers very 



small at Station I and records few after April. Numbers larger and 



oceuTrence more constant at Stations II and III, though frequently 



missing there after August. Maximum in May at both places. No other 



pul.se of particular note. Apparently not very important. 



Fragillaria crotoncnsis Kitton. 



station I Station II Station III Daily Hourly 

 Average 92 4,516 7,888 



Identification satisfactory. Colonies not very large. OccuiTcnce 

 twice at Station I, seven times at Station II at wide intervals and nine 

 times at Station III. The records at Station III are mainly in Sep- 

 tember, October and November. Evidently unimportant here in spite 

 of considerable escape from net in catches. 



Fragillaria spp. 



station I Station II Station III Daily Hourly 

 Average 92 27,832 290 103 



Probably most of those included under this heading belonged to 



F. virescens. Occurrence only twice at Station I. Represented at 



Station II by some fairly large numbers widely scattered. Colonies 



small. Apparently adventitious. 



Gomphonema constrictum Ehrbg. 



Station I Station II Station III Daily Hourly 



Average 1,322 22,094 282 103 8,138 



Identification uncertain. Numbers small. Losses through net heavy. 

 Recorded seven times at Station I at irregular intervals. Well repre- 

 sented in May and June at Station II. Recorded seven times at 

 Station III in very small numbers. 



Gomphonema spp. 



station I Station II Station III Daily Hourly 

 Average 65 6,419 5,000 103 



Under this heading are included some members of this group which 



could not be placed satisfactorily. Probably most of them were G. 



subclavatum. Apparently there were five or six species of this genus 



observed at various times and it probably has some importance though 



it mav be adventitious. 



