688 Transactions of the Society. 



Figs. 13-19 X 830. 

 Fig. 13. — Transverse section No. 2 \ 

 „ 14. „ „ „ 9 



„ 15. „ „ „ 39 > through one and the same valve. 



„ 16. „ „ „ 40 



„ 17. „ „ „ 66 ; 



„ 18.— Portion of the longitudinal section No. 1"! through one and the same 

 „ 19. — Longitudinal section „ 8/ valve. 



„ 20. — Portion of the section No. 8. 



The longitudinal section, fig. 19, corresponds to the dotted line in the 

 transverse sections figs. 15 and 16. In figs. 13, 15, and 16 the more faint contours 

 indicate the outlines of the membrane with slight change of focus, corresponding 

 to the undulations in fig. 19. The small continuation / at the edge of several 

 transverse sections is probably due to the adhesion of the girdle-band. 



The thick longitudinal section fig. 18 comprises nearly the entire wing; the 

 fig. in consequence shows a portion of the wing in surface view, a, the places 

 where both membranes of the fold cling together, corresponding to fig. 14 in 

 transverse section, b, the folds, but not clinging together, i. e. the tubes which 

 connect the cell-lumen with the continuous marginal tube, corresponding to 

 fig. 15 transverse section. 



Figs. 21-22. — Triceratium Favus. 



Fig. 21. — One end of a section going nearly through the middle of a valve. 

 a f, outer surface, i f, inner surface, r I, marginal ridge, n, portion where the 

 section goes through the hexagonal prismatic chambers, consequently touching 

 the chamber-openings k o. w, portion of a section near the edge of a chamber, 

 consequently the vertex shows a connection of the heads of the net-lines. 

 d, spines in the angles between the hexagons, g r, basal membrane. 



Fig. 22. — Similar section, touching the middle of one of the three pro- 

 tuberances. 



Figs. 23-8. — Coscinodiscus radiatus. 



Fig. 23. — Marginal portion of the middle section of a specimen at the moment 

 of division (from the Norwegian coast), g r', basal membrane of the original cell. 

 g r", basal membrane of the valve in process of formation, g h, the girdle-bands. 

 ab s, the nodule of which mentiou is made in the text, p r, protoplasm. 



Fig. 24.— Marginal portion of a middle section through an undivided specimen. 

 The letters have the same signification as in fig. 23. 



Fig. 25. — The first section from the series from which the preceding was 

 taken ; the girdle-band gb in surface view with the very small chambers of the 

 margin r k. 



Fig. 26. — Small portion of the surface view of a specimen (from the marl slate 

 of Oran) focused to the plane indicated by line 1, fig. 23. k 6, chamber openings. 



Fig. 27. — Similar portion with slightly lower focal adjustment, line 2, fig. 23. 



Fig. 28. — Portion of a specimen from the edge with abnormally thick chamber- 

 walls. 



Fig. 29. — Coscinodiscus oculus iridis. 



Small portion of a vertical section, a/, outer surface, if, inner surface of the 

 membrane. 



Fig. 30. — Coscinodiscus centralis. 



Portion of a section through a valve with unusually coarse marking, af, 

 outer surface ; i f, inner surface. 



Fig. 31. — Coscinodiscus concinnus. 



Portion of a thin section ; outer as well as inner surface can only be distin- 

 guished at the common curve (not figm'ed). 



Fig. 32. — Eupodiscus argus. (Omitted.) 



