38 DESMIDS OF THE LWITED STATES. 



P. EUPESTEE, Kg. Plate Y, fig. 13. 



Cells ovate elliptical, length about two diameters ; apices 

 rounded. 



Diameter 20-25 /<. 



Rabenhorst unites the preceding with this form. They are 

 very near in size, but not the same in shape ; the one is more 

 cylindrical and the other inclines more to an ellipse in form. 

 Collected in a mucous gathering on dripping rocks. 



P. Clevei, Lund. Plate LXI, fig. 27. 

 See Calocylindrus. 



P. CEUCIFEEUM, (D. By. ), Wittr. Plate X, figs. 9-11. 



Cells cylindrical, nearly twice as long as wide, scarcely 

 constricted, ends roundly truncate : seen from vertex orbic- 

 ular ; chlorophyl laminae arranged in form of a cross as seen 

 in transverse section ; cytioderm smooth. 

 Syn. Cosmarium cruciferum, D. By. 

 Marsh pools, Florida. 



P. (Cylindrocystis ) TUiriDUM, F. Gay. Plate XLY, figs. 7, 8. 



Cells twice as long as broad; each semi-cell a broadly 

 truncated cone. Cytioderm smooth. 

 Diameter 28 /<. 



Frequent in Tocoi marshes, Florida. 



Genus, CLOSTEEIUM, Nitsch. 



Cells simple, elongated, Innately curved or crescent-shaped, 

 entire, in the center not constricted but frequently marked with 

 from 1-5 transverse striae ; the cytioderm or wall, thin, moder- 

 ately firm, smooth or more or less distinctly striate. 



The chlorophyllous cytioplasm is mostly arranged in longitu- 

 dinal parietal laminae, broken in the middle by a pale transverse 

 band ; at each end there is usually a clear, circular, colorless or 

 straw-colored vesicle, or vacuole, which contains minute granules 

 in constant motion. As the specimen dries the "dancing 

 granules" disappear, and the vesicle vanishes. Compare Intro- 

 duction, page 16. Compare also Addenda. 



A distinct circulation of granules may be noticed in good 

 living specimens. 



The Closterium in normal condition is always green, but may 

 be found of various tints of reddish brown ; these changes of 

 color take place as life becomes extinct. The striated forms 



