68 allan hancock pacific expeditions vol. 3 



Southern Section 



The southern section (south of 25 °N. latitude) is a region of low 

 diatom productivity at least in the seasons during which samples have 

 been collected in four different years. In 1937, one catch of 20,713 

 cells per liter was collected on March 4 off Gorda Point (23°2'N. 

 latitude, 109°30>^'W. longitude-Gorda Banks), and one of 14,707 

 cells on March 8 southeast of San Josef Island. Chaetoceros compressus 

 predominated in the first, C. radicans in the second. No other catch of 

 the thirteen made in this section had as many as 10,000 cells. Two 

 contained no cells. One catch made farther south along the coast of 

 Mexico (22°16'N. latitude, 106°W. longitude) on April 2 yielded 

 55,125 cells per liter (47,250 cells Nitzschia seriata). 



In 1921, two catches in this section yielded over 100,000 cells per 

 liter. One of these was taken on April 12 southwest of Espiritu Santo 

 Island. Chaetoceros species was listed as predominating. The other was 

 collected on June 9 northwest of the same Island. Thalassionema 

 nitzschioides and Chaetoceros species were most abundant. One catch, 

 taken south of Espiritu Santo on April 11, had 22,656 cells per liter. 

 No other sample yielded as many as 10,000 cells per liter. Three of 

 the twenty-five contained no cells. 



Fifteen of the twenty-five samples collected by the Templeton 

 Crocker 1935 Expedition in this section during November contained no 

 cells. The largest catch was one of 532 cells. 



None of the twenty-four catches of the 1936 series was large. Only 

 one sample had over 3,000 cells per liter, six had none. The largest 

 catch, 19,824 cells per liter, was taken about fifteen miles east of 

 Ceralbo Island. Chaetoceros compressus was the important species nu- 

 merically in this sample. 



Ocean Catches 



Seven catches were made on the southward run to the Gulf. The 

 largest, 919,962 cells per liter, was collected off Point San Juanico 

 (26°14'N. latitude, 112°28'W. longitude). A second large catch was 

 taken north of Cape San Lazaro (25°10'N. latitude, 112°19'W. longi- 

 tude). The estimated number of diatoms was 331,297 cells per liter. 

 In both cases Chaetoceros costatus was the leading species (855,128 

 cells in the first sample, 211,584 cells in the second) with C. curvisetus 

 second in abundance. The other five catches were small, one nearly 



