76 



MICROSCOPY FOR BEGINNERS. 



m. Angles obtuse, acute, or with horn-like prolonga- 

 tions. Staurdstrum, 12* 



1. DlDYMOPRITJM. 



Each cell in the band longer than broad ; two round- 

 ed or angular teeth on each narrow end ; case or sheath 

 distinct, colorless. D. Gremllii, Fig. 17. 



Fig. IT. Didym6prium Grevillii. Fig. IS. Spbserozosma pnlchra. 



2. SPH^EROZOSMA. 



Each cell in the band about twice as long as broad, 

 divided on both ends almost to the middle ; sheath large, 

 colorless. Three cells are shown in the figure. S. pul- 

 chra, Fig. 18. 



3. HYALOTHECA. 



The ribbons are often very long, and the narrow ends 

 of each cell are sometimes slightly constricted, as shown 

 in the lower part of the figure, but the depression is 

 never deep enough to form teeth ; sheath colorless. H. 

 dissiliens, Fig. 19. 



Fig. 19.-IIyalotheca dissiliens. Fig. 20. Bambnsina Brebissunii. 



4. BAMBUSINA. 

 The cells somewhat resemble barrels or casks joined 



