FIGURES 10-18 



Fig. 10. Frequency distribution of the x-ratios in 144 random specimens related to 

 P. depressum Bailey. O, P. depressum ; x, P. oceanicum ; • , var. parallelum ; ■ , var. 

 tenellum. 



Fig. 11. Frequency distribution of length classes in 170 random specimens related to 

 P. depressum . 



Fig. 12. Frequency distribution of the diameter classes in 170 random specimens 

 related to P. depressum. 



Fig. 13. Frequency distribution of the h/d classes in 170 random specimens related 

 to P. depressum . 



Fig. 14. Peridinium depressum Bailey. A, in "resting" position in bottom of drop of 

 mounting medium; B, ventral view; C, left side view; D, apical view; E, dorsal view; F, 

 antapical view. Magnification: x 170. 



Fig. 15. Apex of P. depressum Bailey. A, intact; B, plates separated. Symbols: ap, 

 apical pore; app, apical pore platelet; apl-ap4, first to fourth apical plates; dl, dorsal seg- 

 ment of apical list; lal, left segment of apical list; 111, left lateral list; ral, right segment of 

 apical list; rll, right lateral list; vap, ventral apical platelet. Magnification: x 670. 



Fig. 16. Girdle of P. depressum Bailey. A, intact. Symbols: iz, intercalary zone; 

 s, sulcus; lg-4g, first to fourth girdle plates. B, section showing strengthening ridges. C, 

 cross section showing attachment to adjacent plate and cingular list. Symbols: bp, body plate; 

 cl, cingular list; g, girdle plate. Magnification: A, x 230; B and C, x 470. 



Fig. 17. Ventral area of P. depi essum Bailey. A, ventral view intact; B, left ventral 

 view intact, membranes not shown; C, ventral view showing plates separated. Magnification: 

 X 400. Symbols: acl, anterior cingular list; ag, anterior flagellar groove; agl, anterior groove 

 list; antl, first antapical plate; ant2, second antapical plate; apl, first apical plate; app, ante- 

 rior pore process; arl, anterior right sulcal list; as, anterior sulcal plate; iz, intercalary 

 zone; 11, left sulcal list; Is, left sulcal plate; m, membrane; p, flagellar pore; pas, posterior 

 accessory sulcal plate; pel, posterior cingular list; pg, posterior flagellar groove; pgl, poste- 

 rior groove list; pi, posterior sulcal list; pol, first postcingular plate; po5, fifth postcingular 

 plate; ppp, posterior pore process; prl, first precingular plate; pr7, seventh precingular 

 plate; prl, posterior right sulcal list; ps, posterior sulcal plate; ras, right accessory sulcal 

 list; ris, right internal sulcal plate; rs, right sulcal plate; Ig, 2g, 4g, first, second, anri 

 fourth girdle plates. 



Fig. 18. Details of ventral area. A, left side view with left sulcal plate removed; B, 

 same with plates separated; C, posterior view of cross section of posterior end of sulcus; D, 

 anterior view of cross section of right sulcal plate. Magnification: A and B, x 730; C and D, 

 X 400. (Symbols as in fig. 17.) 



98 



