NO. 5 CUPP AND ALLEN : PLANKTON DIATOMS 69 



10,000 cells, the others less than 1,500 cells per liter. Allen (1934) 

 mentions Chaetoceros costatus as a prominent species south of Point 

 Abreojos in April, 1931. About 2,000,000 cells per liter were recorded 

 for one catch. 



Genera and Species of Diatoms 



Sixty-seven species of diatoms distributed among thirty-one genera 

 were found in the samples from the Gulf during the routine counting. 

 In the entire series sixty-nine species in thirty-two genera were recorded. 

 Of this number, fourteen species were of considerable importance, seven 

 reached sufficiently large numbers to be given rank as of major im- 

 portance. The one most abundant species, Chaetoceros radicans, was 

 more than five and one-half times more numerous than any other species. 



Forty-one of the sixty-seven diatoms found in the Gulf were neritic 

 species. Five were tychopelagic (semibottom living littoral diatoms that 

 have been broken away from their substratum) , fifteen were oceanic, and 

 six were unclassified. Northerly and southerly temperate neritic species 

 were present in equal numbers. Table 2 lists all species of diatoms 

 according to their habitat groups and indicates the most important 

 species. 



TABLE 2 

 Species of Diatoms 

 OCEANIC 



Arctic 



1. Chaetoceros atlanticus CI. (and boreal) (Fig. 22) 



2. decipiens CI. (and boreal) 



3. Thalassiothrix longissima CI. and Grun. (Fig. 40) 



Temperate 



L Asteromphalus heptactis (Breb.) Ralfs (Fig. 6) 



*2. Bacteriastrum elongatum CI. (southerly) (Fig. 21) 



3. Chaetoceros peruvianas Brightw. (and tropical) 



4. Corethron hystrix CI. (Fig. 7) 



5. Hemiaulus hauckii Grun. (and tropical) 



6. Rhizosolenia alata Brightw. (Fig. 18) 



7. alata f. indica (Perag.) Osten. 



(south temperate or subtropical) (Fig. 19) 



8. bergonii Perag. (Fig. 11) 



9. styliformis van longispina Hust. (northerly) (Fig. 15) 

 10. Thalassiothrix frauenfeldii Grun. (Fig. 41) 



