1911] Kofoid: Go)njaulax catenata. 289 



Levander seems to have represented the relations of the anta- 

 pical and posterior furrow plate in different fashion from that 

 portrayed in my figure. 



The plate formula for Peridinium steiiii as determined by me 

 (1909) and that of Gonyaulax spinifera and G. polyedra and of 

 Levander's Peridinium catoialum are given below. 



Table op Plate Formulas 



The essential likeness of P. catenatum to Gonyaidax and its 

 dissimilarity to Peridinium is at once apparent in the table. A 

 detailed examination only serves to emphasize these conclusions, 

 as follows : 



The apical plates of Peridinium show marked uniformity and 

 bilateral symmetry (See Stein, 1883, pis. 9-11, and Kofoid, 1909, 

 pi. 2, fig. 1) while those of Gonyaulax (see preceding paper, pis. 

 9-17) usually show marked irregularities in size and position and 

 also decided bilateral asymmetry which is usually more marked 

 in the dorsal region and left face. This is also true of Levander's 

 species. Apical 1' is not a subsymmetrical rhomb plate as in 

 Peridinium but an asymmetrical narrow plate strikingly like 

 that in Gonyaulax, running from the anterior margin of the 

 anterior plate of the ventral area to the apex where it is con- 

 nected with a small closing platelet (cl. pi., pi. 18, fig. 2) just as 

 in Gonyaulax. Again in Peridinium the anterior intercalaries 

 are symmetrically placed mid-dorsal plates two or three in num- 

 ber, and of approximately equal size, or placed in nearly a 

 bilaterally balanced relation. In Levander's species they (^''-i") 

 are irregular in size and lie somewhat upon the right dorsal 

 shoulder, again just as in Gonyaulax, especially G. polyedra (see 

 preceding paper, pi. 12, fig. 20.). 



There are six precingulars {l"-6") in Levander's species and 

 in all species of Gonyaulax, and seven in Peridinium. JMoreover 



