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University of California Puhlications in Zoology [Vol. 18 



an ascending spiral. It is not therefore such a reversal as that noted 

 in the figures of Daday (1888) and Lebour (1917) and involved in 

 the orientation of ErytJiropsis proposed by Faure-Fremiet (1914). 



The transverse flagelluni and the girdle have important and fixed 

 relations to the process of binary fission. The fission plane passes 



fiss. ] 



aft. ar. 



Fig. 5. Ventral view of Ceratium furca. X 706. In this and the following 

 figure the apical plates are numbered l'-4', the preeingulars l"-4", the post- 

 cingulars l"'-5"', the antapicals i""-2"", and the girdle plates 1-4; att. ar., 

 attachment area; fiss. I., fission line; v. a., ventral area. 



Fig. 6. Dorsal view of C. furca. X 706. 



through the point of origin of the transverse flagelluni and cuts across 

 the girdle obliquely from the right anteriorly to the left posteriorly, 

 parting the theca along definite suture lines (figs. 5, 6). 



This plane has this oblique position in the dinoflagellates generally 

 except in the Prorocentridae and the Dinophysidae. A reversal of 



