DESMIDS, DIATOMS, AND FRESH-WATER ALGjE. 77 



therefore, applying equally well to the other. There 

 are more than forty species of the genus. The readet 

 must expect to find many forms not included in this 

 list, which contains only some of the most common in 

 the writer's vicinity. 



a. 



Some Species of Micraste'rias. 



More or less circular in outline (a). 



Not circular; divided into radiating arms (b). 



Not circular; not divided into arms; central slit 

 gaping' (f). 



Each semi-cell divided 

 by four deep cuts into 

 one terminal and four 

 side-lobes, each side- 

 lobe divided by a 

 shorter incision into 

 two sections, each sec- 

 tion by a still shorter 

 cut divided into two 

 divisions, each division 

 by a yet shorter cut 

 divided into two parts, 

 and each part with 



two teeth. Desmid very large. M. radidsa, 

 Fig. 32. 



Each semi-cell divided by four incisions into one 

 end-lobe and four side-lobes,- each side-lobe 

 divided by a shorter cut into two parts and each 

 part with two teeth. End-lobes often dentate. 

 M. rothta, Fig. 33. 



Fig 32. — Micrast^rias radi6sa. 



