1922] Allen: Studies on Diatoms and Dmoflagellates 375 



sp. these two were, with Nitzschia ,s< riata CI. and Ckaetoceras curvi- 

 setum CI., the conspicuous forms at Pt. Hueneme. 



So far as we know at present Nitzschia seriata CI. and Chaetoceras 

 curvisetum CI. may constitute a fairly stable portion of the diatom 

 population in the southern California region and forms such as 

 Bacteriastrum varians Lauder, Leptocylindrus danicus CI., Eucampia 

 zoodiacus Ehr., and Thalassiosira baltica Grun may be more typically 

 variable, or fluctuating or delicately responsive in character, and so 

 more truly indicatory of the incidence and influence of changes in 

 their environment. 



Dinoflagellates showed general features of seasonal distribution of 

 species essentially similar to those of diatoms. At La Jolla eight 

 forms attained prominence in one or more of the productive periods 

 sufficient to place them amongst the first three species in one or more 

 weeks. One of the most prominent of these eight was a catchall 

 assemblage called Gymnodinium sp. which may at times have included 

 many other minute organisms. In that respect the group is even more 

 unsatisfactory than Chaetoceras sp. Two of the other prominent 

 forms, Peridinium cerasus Pauls, and Peridinium minutum Kof., were 

 often indistinct and hence not satisfactorily identified. Several small 

 species may have been recorded under those designations at one time 

 or another. 



Of the five prominent species identified with approximate accuracy, 

 Prorocentrum micans Ehr. was decidedly the most persistent, reaching 

 third place or better in nine out of the ten noticeably productive 

 weeks. In addition to it Ceratium furca (Ehr.) Clap. u. Lach. and 

 Peridinium minutum Kof. were notably abundant in one or more 

 weeks. 



At Pt. Hueneme fourteen weeks were relatively productive in 

 which six forms, besides Gymnodinium sp., were amongst the three 

 most abundant in one or more weeks. Of these only four reached 

 numbers large enough (3000 per liter or more) to be considered dis- 

 tinctive. They were Prorocentrum micans Ehr., listed amongst the 

 first three in all of the fourteen weeks; Ceratium furca (Ehr.) Clap, 

 u. Lach. amongst the first three in four weeks; Ceratium tripos 

 (O.F.M.) Nitzsch. amongst the first three in three weeks; and 

 Peridinium minutum Kof. amongst the first three in seven weeks. 



As in the case of diatoms it appears probable that one or two 

 species are relatively stable in the region studied and that others are 



