PLATE 2. 



Figs. 15-17. Ceratium hirmdinella (0. Miill.) Sclirank, var. brachijcems (v. Dad.) 

 Ostf. Fig. 15, seen in dorsal view and a little from antapex ; Fig. IG, 

 seen from the left side and a little from antapex ; Fig. 17, cell witli con- 

 tents in ventral view. 



Figs. 18-22. Melosira Agassizii, sp. nov. Fig. 18, part of a filament with termi- 

 nal cell, showing wall structure ; Fig. 20, diagrammatic drawing of a 

 filament with large liyaline girdle parts ; Fig. 19, two cells witli con- 

 tents ; Fig. 21, three cells in divisions ; Fig. 22, two cells with recently 

 completed division. 



Zeiss's apochromatic objectives and compensation oculars. 



