414 



University of California Publications in Zoology [Vol. 22 



throughout the twenty hours. Dinoflagellates were also studied, but 

 they were few in numbers and showed nothing of evident importance. 

 Mission Bay occupies at high tide an area of nearly or about four 

 square miles. At low tide it is reduced to channels and lagoons of 

 less than half that extent. The deepest point at high tide is not far 

 from the entrance according to the U. S. Coast and Geodetic Chart 

 for 1902, which records twenty-eight feet. It is doubtful if any point 

 so deep as that is to be found now. The mean depth at high tide is 



Fj£L Graph to shov half-hourly distribution of Diatoms 

 in tide-vater at Mission Bay Bridge , Nov 3-4,1923 



Temperature q^ 



Specific r •~^.*— — ■' 



Gravil-jj 



Dial-oms 



©"•"^••o^U^o 



probably not more than three or four feet. The entrance is narrow 

 and the tidal flow correspondingly rapid. For a period of six months 

 or more preceding the time of taking these collections there had been 

 no rain and it had probably been four months since any fresh water 

 drained into this bay. 



The accompanying graph (fig. 1) shows the character of the varia- 

 tions in successive half-hours under the five conditions investigated. 

 Each curve is correctly drawn to scale, though the scales are not 

 indicated in this figure. The diatom curve was plotted on semi- 

 logarithmic paper. As shown by the tidal curve, the records begin 

 just before high tide in the evening and run to low tide the next after- 

 noon. The influence of the tide upon specific gravity and the number 



