422 



University of California Publications in Zoology [Vol. 18 



observations have not followed every step of exuviation and regenera- 

 tion of the shell under controlled conditions, it is presumed that the 

 plate arrangements of the shell ordinarily are not changed during 

 this ecdysis unless unusual environmental changes are encountered. 

 The uniformity of the plate pattern in chains of individuals found for 



Fig. 18. — Chart of measurements of critical sutures of the dorsal epithecal 

 plate patterns for 44 and 46 specimens of Peridinium divergens Ehrbg., i.e., 

 for the sutures between plates \a and 4" on the left and .3a and 4" on the right. 



