DESMIDS, DIATOMS, AND FRESH-WATER AtGJE. 75 



i. Ventrum nearly straight^ body tapering toward 

 the rounded, sometimes curved, ends; vacuoles 

 small, often scarcely visible. C.juncidum, Fig. 23. 



Fig. 23. — Clost6rium juncidum. 



b. Ventrum and back equally curved; ends tapering; 



from ten to fourteen chlorophyl globules in a 

 central, longitudinal row in each semi-cell; 

 vacuoles very small. C. acerdsum, Fig. 24. 



c. Ends rounded ; chlorophyl often arranged in nar- 



Fig. 24. — Closterium acer6sum 



row, longitudinal bands; chlorophyl globules 

 numerous; vacuoles near the ends; cell very 

 large. C. Ltinula, Fig. 25. 



Fig. 25. — Closterium Lunula. 



d. Ends rounded ; chlorophyl often arranged in nar- 

 row, longitudinal bands ; chlorophyl globules of- 

 ten numerous; vacuoles close to the ends. C. 

 Ehrenb^rgii, Fig. 26. 



Fig. 26. — Closterium Ehrenbergii. 



Fig. 27. — Closterium acuminatum. 



