1924 ] 
Allen: Marine Diatoms and Dinoflagellates 
245 
these had already been observed in the catches made by McEwen 
and Mortensen in 1920 (Allen, 1922). In the main, the same forms 
tended to prominence, although Nitzschia seriata Cl. was much less 
conspicuous than in the catches of 1920. Only in the Santa Barbara 
region did this species attain a place in the list of five most abundant 
forms. 
Eight genera represented by ten species were found to be among 
the five most numerous forms in one or more regions. Of these, the 
most prominent numerically was Skeletonema costatum (Grev), which 
occupied first place in four regions out of the six in which it was 
conspicuous. The genus Chaetoceras was second to Skeletonema only 
in numbers. In constancy of representation, it was, as usual, first. 
The specimens of this genus were mostly small and difficult to segre¬ 
gate, for which reasons the record is somewhat unsatisfactory. Small 
forms listed as Chaetoceras sp. were found in all regions. In addition, 
Chaetoceras debile Cl. (sometimes including Civ. curvisetum Cl.) and 
Chaetoceras scolopendra (Cl.) were notable in some regions. In this 
particular series, the genus Chaetoceras appears to be relatively much 
more prominent south of Monterey than in any region farther north. 
The genus third in prominence in this series was Thalassiosira. 
Identification of the species was not fully satisfactory. Only two, 
Thalassiosira baltica (Grun) and Th. gravida Cl., were recorded 
although there may have been as many as four or five species present 
in some catches. This genus showed some prominence in the southerly 
regions, but it was so very abundant in the regions of Columbia River, 
Destruction Island, and Puget Sound as to suggest the idea that 
northerly conditions especially favor it. 
Asterionella was more conspicuous than in most series and it was 
especially noticeable near San Francisco. Heretofore, only one 
species of this genus had been noticed, Asterionella japonica Cl., 
but in the course of study it became evident that another species, 
Asterionella kariana Grun, was also present. This species seems to 
be very fragile in many colonies, all the distal points of the cells 
being broken. This breakage probably led to more or less error in 
identification even after the presence of a second (and possibly a 
third) species was recognized, but it is very probable that A. japonica 
Cl. is, in this series, more prominent in the southerly regions, while 
A. kariana Grun is more prominent in the northerly regions. 
Bacteriastrum, Grammatophora, and Eucampia are the other three 
genera which had representatives among the five most prominent 
