84 MICROSCOPY FOR BEGINNERS. 



a. Sides wavy, gradually expanding towards the cen- 

 tral cut. E. didelta, Fig. 41. 



a. Sides hardly wavy, suddenly expanding towards 

 the central cut. Small. E. ansdtum, Fig. 42. 



9. TETMEMORCS (Figs. 43, 44). 



1. Widest in the middle, the ends tapering. T. granu- 



Idtus, Fig. 43. 



Fig. 43. Tetmemorus granuldtus. Fig. 44. Tetmfimorus Brebiss6nii. 



2. Not widest in the middle, the ends not tapering. T. 



reliss6nii, Fig. 44. 



10. DOCIDIUM (Figs. 45, 46). 



1. A rounded enlargement on each side of the central 

 constriction. D. Bdculum, Fig. 45. 



Fig. 45. Docidinm Bacnlum. Fig. 46. Docidium crennlatum. 



2. Two or more small enlargements on each side of the 

 central constriction, giving the edges a wavy ap- 

 pearance. D. crenulatum. Fig. 46. 



11. COSMAKIUM (Figs. 47, 48, 49, 50). 



The ends of Cosmarium are never notched nor in- 

 cised. They may be, and often are, rough or warty, 

 hut the ends are always entire. There are about one 

 hundred species. The following are common : 

 1. Surface smooth ; cell less than twice as long as broad, 



