8o 



AQUATIC MICROSCOPY FOR BEGINNERS. 



never circular as in Micrastdrias, and the margins are 



wavy, never sharply toothed. The ends are usually 



notched. There are about forty species. 



I. Each half-cell oblong; an end-lobe present in 

 both halves, and formed by a short rounded 

 incision 01 each side. E. crdssum, Fig. 40. 



Fig. 40. — EuAstrum 

 crassum. 



Fig. 41. — Eudstrum Fig. 4a. — Euastrum- 

 did^lta. ansdtum. 



2. Each half-cell somewhat triangular, without 

 distinct end-lobes (a). 



a. Sides wavy, gradually expanding towards the cen- 

 tral incision. E. dide'lta, Fig. 41. 



a. Sides hardly wavy, suddenly expanding towards 

 the central incision. Small. E. ansdtum, Fig. 

 42. 



9. Tetm^morus (Figs. 43, 44). 

 I. Widest in the middle, the ends tapering. T. 

 granuldtus, Fig. 43. 



D 



Fig, 43. — Tetmemorus granuldtus. 



Fig. 44, — Tetmemorus Brebis56n 



