NO. 5 CUPP AND ALLEN : PLANKTON DIATOMS 63 



only five catches out of eighty (6.3%) had over 100,000 cells per 

 liter, with the largest catch estimated at 217,476 cells. Fourteen catches 

 in 1937, three in 1921, and eleven in 1936, yielded no cells. 



Northern Section 



Three regions in the northern section were particularly noteworthy 

 for their high diatom productivity. The first and largest of these three 

 was found on the west side of the Gulf to the north of Angel de la 

 Guardia Island, between 29°30'N. and 30°N. latitude; the second 

 region off the southeastern part of Tiburon Island on the east side of 

 the Gulf in 28°49'N. latitude, 112°16'W. longitude; and the third 

 region on the east side of the Gulf from 27°56'N, (off Guaymas) 

 south to 27°3rN. latitude. (Shaded areas on Map 1) 



Nine catches in the first named region to the north of Angel de la 

 Guardia contained over 100,000 cells to the liter with five of these 

 having over one million cells. The largest catch in the entire series 

 was taken a few miles northwest of the Island on March 22. It was 

 estimated that the yield from this one catch was 5,058,800 cells per liter. 

 Of this number, 4,945,000 cells (4,460,000 in good condition, 485,000 

 in poor condition) belonged to the one species, Chaetoceros radicans. 

 This species predominated in all of the nine large catches. 



In the three catches off Tiburon Island, one gave nearly 2,000,000 

 cells per liter, one nearly 3,000,000 cells, and the third 408,000 cells. 

 Chaetoceros species was most abundant in the two largest, Chaetoceros 

 socialis in the third. A catch to the south of the Island (28°4rN. lati- 

 tude, 112°27'W. longitude) had 12,125 cells per liter. 



In the third region, two catches off Point Doble contained 1,021,750 

 and 1,950,140 cells with Chaetoceros compressus and C. species predomi- 

 nating, respectively. The third large catch in this region was estimated 

 to have 3,300,500 cells per liter, with 2,465,000 of these Chaetoceros 

 radicans. 



Table 1 (pp. 66 and 67) gives the data for all the catches over 

 100,000 cells per liter taken in the northern section of the Gulf. 



No large catches were taken in the Gulf north of 30°N. One 

 sample had 7,875 cells per liter, four between 1,000 and 3,000, two 

 between 125 and 250, and one had no cells. Two other catches on the 

 east side of the Gulf opposite the Angel de la Guardia region of 

 abundance showed no cells. Three catches taken near the west side of 



