DESMIDS, DIATOMS, AND FRESH-WATER ALGM. 79 



i. Each semi-cell divided by two acute depressions 

 into one end-lobe and two side-lobes, each side- 

 lobe divided by an acute depression into two 

 short parts, each part divided by an acute depres- 

 sion into two short arms, and each arm with two 

 teeth; arms of the end-lobes each with two teeth; 

 the whole desmid with twenty short arms. M. 

 dichdtoma, Fig. 36. 



Fig. 3B. — Micrast^rias dscitans. Fig. 39. — Micrast^rias liticeps. 



c. Divided into one end-lobe 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. KitcMlii, Fig. 



37- 



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

 ing beyond the end-lobes; terminal lobes some- 

 times notched laterally, as shown in the figure, 

 sometimes not. M. dscitans, 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 almost divided into two halves by a 

 central slit across the middle, but the cell outline is 



