NO. 5 CUPP AND ALLEN : PLANKTON DIATOMS 65 



catches of 217,476 cells, 118,860 cells, and 95,577 cells per liter were 

 collected just south of Tiburon on March 10 and 11. Chaetoceros 

 species, C. debilis, C. compressus, C. curvisetus, and C. constrictus were 

 present in largest numbers. One large catch (143,724 cells) was taken 

 in mid-Gulf about seventy miles southeast of Tiburon on March 12. 

 Almost the entire catch was made up of Thalassiothrix heteromorpha{ ?). 



Middle Section 



With two exceptions, the middle section of the Gulf (25°N. to 

 27 °N. latitude) was a region of very low diatom productivity in 1937. 

 One catch of 29,337 cells per liter was made in Concepcion Bay on 

 March 15. Nitzschia seriata, Chaetoceros species, and C. curvisetus 

 were most abundant. The other large catch, taken off Topolobampo 

 Bay on March 31, contained 512,000 cells per liter. Here Skeletonema 

 costatum, Nitzschia seriata, and Eucampia zoodiacus were most numer- 

 ous. Nine of the seventeen catches in this section yielded no cells. The 

 remaining six were all very small. 



In 1921, large catches were found in the Carmen Island region on 

 May 19 and 23 (480,610 cells and 264,385 cells) and on June 13 and 

 14 (338,156 cells and 450,740 cells). Chaetoceros species and C. com- 

 pressus were most abundant. One catch of 85,645 cells (Rhizosolenia 

 stolterfothii, Chaetoceros debilis, and C. decipiens) was taken in San 

 Nicolas Bay on May 17, and one of 142,920 cells (Chaetoceros species, 

 Bacteriastru7n elongatum, and Thalassionema nitzschioides) on April 

 13 in mid-Gulf off San Nicolas Bay. 



Four catches at two stations in mid-Gulf a little north of the lati- 

 tude of Topolobampo Bay and one in Concepcion Bay were the only 

 catches of moderate size in the middle section during 1936. Of these 

 the largest was only 39,396 cells per liter, the smallest 11,970 cells. 

 Chaetoceros species was most prominent in the mid-Gulf catches, 

 Thalassiothrix heteromorpha (?) in the Concepcion Bay catch. These 

 catches were all taken between March 14 and March 19. 



The Templeton Crocker Expedition of the California Academy of 

 Sciences of November, 1935, collected six plankton samples in the 

 middle section of the Gulf. One of these, taken a short distance south- 

 west of Topolobampo Bay on November 16, was a large catch of 

 106,019 cells per liter. Of these, 82,316 cells belonged to the one 

 species, Chaetoceros curvisetus. The other five catches were small. 



