76 AQUATIC MICROSCOPY FOR BEGINNERS. 



e. Large, crescent-shaped; center broad, ends 



acute, vacuoles small. C. acumindtum, Fig. 27. 

 e. Small, crescent-shaped, distance between the 



ends about ten times the central diameter; 



center narrow, vacuoles indistinct. C. Diana, 



Fig. 28. 



Fig. 28. — Clost^rium Didnse. Fig 29. — Closterijim ViSnus 



e. Very small, crescent-shaped, from eight to twelve 

 times as long as broad; center narrow, ends 

 sharp, vacuoles distinct. C. Venus, Fig. 29. 



/. Each beak about as long as the green body, 

 sometimes shorter; whole cell slightly curved; 

 vacuoles usually indistinct. C. rostrdtum. Fig. 

 3°- 



Fia;. 30. — Clost^rium rostrdtum. 



/. Each beak exceedingly fine, longer than the 

 ■spindle-shaped green body, the tips alone; 

 curved. - C. setdceum, Fig. 31. 



Fig. 31. — Clostdrium setdceum. 

 7. MlCRASXfiRIAS (Figs. 32 to 39). 



Each Micrasterias is incompletely divided across 

 the middle into two equal and similar halves, or semi- 

 cells, by a deep slit, the sides of which may be either 

 close together or somewhat separated. The margins 

 of both semi-cells are also much incised and notched, 

 but both in the same way, the description of one-half, 



