1918] Barroivs: Skeletal Variations in the Genus Peridinium 415 



discussed, and to be second only in its significance to the presence of 

 the skeleton itself. The facts that the skeleton throughout the whole 

 group of Peridinidae is found to be divided into plates, that through- 



Fig. 17. — Chart of measurements of critical sutures of the ventral epithecal 

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

 the sutures between plates 1' and 2" on the left and between 4' and 7" on the 

 right. Note that from the distribution of the specimens measured, as shown 

 in the charts for geographic races, there is nothing to indicate a cause for the 

 double or triple crests either in these charts or in those of figure 18. This 

 multiplicity of the crests must, therefore, be regarded as purely accidental. 



