NO. 5 CUPP AND ALLEN : PLANKTON DIATOMS 73 



to the Gulf of California. Seven of these were taken in the open ocean 

 ofi Lower California, sixtj-six in the Gulf. 



2. In the northern section of the Gulf (north of 27 °N. latitude) 

 three regions were notably productive of diatom growth: 



a. the west side of the Gulf to the north of Angel de la 

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



b. the east side of the Gulf off the southeastern part of Ti- 

 buron Island; 



c. the east side of the Gulf between 27°56' and 27°31'N. 

 latitude. 



3. Regions a and b were also highly productive in 1921 and 1936, 

 indicating that these localities may be peculiarly favorable for diatoms. 



4. The high productivity of the upper third of the Gulf may very 

 probably be due, in large part, to the influence of the Colorado River. 



5. The middle section of the Gulf (between 25° and 27°N. lati- 

 tude), except for one catch in Concepcion Bay and one off Topolobampo 

 Bay, was poor in diatom growth. The favorable influence of land and 

 shallow water may account, at least in part, for the higher catch in 

 Concepcion Bay. Productivity around Carmen Island, unlike that in 

 1921, was poor in 1937. 



6. The southern section of the Gulf (south of 25 °N. latitude) 

 is a region of low diatom productivity according to results from four 

 Expeditions. 



7. Sixty-seven species of diatoms distributed among thirty-one 

 genera were present in the samples from the Gulf. 



8. Neritic species of northerly and southerly temperate habitats 

 predominated. 



9. Chaetoceros radicans, C. species, Skeletonema costatum, Chaeto- 

 ceros compressuSj C. socialis, and C, debilts were the most prominent 

 species. Chaetoceros radicans occurred in very large numbers in nine 

 catches taken off Angel de la Guardia Island. 



10. The species of diatoms found in the Gulf vary little from 

 those in the open ocean off Lower California or at La Jolla. 



11. While the percentage of cells in good condition was not so 

 high as in 1936, a remarkably large percentage were in good condition. 



12. Much more information as to physical, chemical, and meteoro- 

 logical conditions in the Gulf is needed before we can properly interpret 

 the results of these diatom studies. 



