PLATE 2. 



Figs. 15-17. Ceratium hirundinella (0. Mull.) Sclirank, var. brachi/ceras (v. Dad.) 

 Ostf. Fig. 15, seen in dorsal view and a little from ant apex ; Fig. 16, 

 seen from the left side and a little from antapex ; Fig. 17, cell with 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 hyaline girdle parts ; Fig. 19, two cells with con- 

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

 completed division. 



Fi s s - 15 " 17 - oiTTo' Fi e- 18 - o^Nb' Fi s- 20 - o^TTo' ¥ '^ 9 > »■ 22 > oiTllP 11 



Zeiss's apochromatic objectives and compensation oculars. 



