DESMIDS, DIATOMS, AND FRESH-WATER ALGM. 83 



c. Divided into one end and two side lobes (d). 



d. Side -lobes divided by a shallow notch into two 



parts extending beyond the end-lobes, each part 

 with two teeth on both ends. M. Kitchelii, Fig. 

 37. 



d. Side-lobes not divided into two parts, but extend- 

 ing beyond the end-lobes. M. oscitans, Fig. 38. 



d. Side-lobes not divided into two parts, not extend- 

 ing beyond the end-lobes. M. Idticeps, Fig. 39. 



8. EUASTRUM (Figs. 40, 41, 42). 



Euastrum is divided into two halves by a central slit 

 across the middle, but the cell is never circular as in 

 Micrasterias, and the margins are wavy, never sharply 

 toothed. The ends are usually notched. There are 

 about forty species. 



1. Each half oblong ; an end-lobe present in both halves, 

 and formed by a short rounded cut on each side. 

 E. cmssum, Fig. 4.0. 



Fig. 40. Ea&strura cris- Fig. 41 Enastrum Fig. 42. Euastrum 



sum. didelta. ansatnm. 



2. Each half somewhat triangular, without distinct end- 

 lobes (a). 



