' I.' N5TERTFM. 37 



P. CBA8SA, D.By. Plate \', fig. 3. 



Cells short, ovate-cylindrical, H-2 times as lonp- a> wide, 

 chlorophyl not separated, but concentrated into two or more 



nuclei in each cell. 



Diameter 25-29 ,". 



Collected by E. 8. Cheeseman, Knowlesville, New York, 

 in gelatinous mucus in an aquarium. 



P. rupestre, Kg. Plate V, fig. 13. 



Cells ovate elliptical, length about two diameters; apices 

 rounded. 



I diameter 2( I 25 ". 



Rabenhorst unites the preceding with this form. They are 

 very near in Bize, l>ut not the same in Bhape, tin- one is mure 

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

 Collected in n mucous gathering on dripping ruck-. 



P. ( i i:\ r.i. Lund. Plate L, fig. 27. 

 See i alocylindrus. 



ua, CLOSTERIUM, Nitsch. 



( Jells Bimple, elongated, lunatelv curved or crescent-shaped, entire, 

 In the centre 1 1< >t constricted but frequently marked with from L 5 

 transverse striae; the cytioderm or wall, thin, moderately firm, 



-i ill or more or less distinctly striate. 



The chlorophyl lous cytioplasm is mostly arranged in longitudinal 

 parietal lamina?, broken in the middle by a pale transverse band ; 

 at each c\u\ there is usually a clear, circular, colorless <>r straw- 

 colored vesicle, or vacuole, which contains minute granules in 

 constant motion. A- the specimen dries the "dancing granules" 

 disappear, and tin- vesicle vanishes. ( Compare Introduction, page Ifi. 



A distinct circulation of Granules mav be noticed in srood living 

 specimens. 



The Closterium in normal condition i- always green, but may bo 

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

 take plaoe as life become- extinct. The striated forms have a firm 

 cytioderm and retain their outline when dry or empty; others, not 

 striated are more flexible and collapse when dried. The chlorophyl 

 escapes by a slight separation of the semi-cells, and leaves the case 

 colorless, 



