94 BRITISH DESMIDIACEJ3. 



f Cells with one process only at each angle of the cell. 



Cells not more than four times as long as broad, 



excluding the processes. 

 Cells in vertical view 2-5-radiate ; if more than 



4-radiate, processes relatively short. 

 a. Faces of semicell smooth or provided with 

 granules or small dentieulations ; con- 

 spicuous verruca? never present except 

 on the apex of the semicell. 

 A. Processes well developed, at least as 

 long as the body of the cell is 

 broad, and frequently longer ; 

 semicells usually distinctly cuneate 

 or cup-shaped, bearing the pro- 

 cesses at the upper angles of 

 the cells. 



1. Cells fairly large, more than 

 20 /x long excluding the pro- 

 cesses. 



111. St. gracile. 



112. St. paradoxum. 



113. St. pseudopelagicum. 



114. St. inflexum. 



115. St. crenulatum. 



116. St. neglectum. 



117. St. dubium. 



118. St. boreale. 



119. St. Pseudosebaldi. 



120. St. Manfeldtii. 



121. St. Diiacense. 



122. St. bicorne. 



2. Cells small, less than 20 /x long, 

 excluding the processes. 



123. St. subgradllinmm. 



124. St. tetracerum. 



125. St. iotanum. 



126. St. pseudotefracerum. 



127. St. micron. 



128. St. latiusculum. 



B. Processes only feebly developed, not 

 as long as the body of the cell is 

 broad. 



1. Processes solid, deeply bifid at 



their apices. 



129. St. pelagicum. 



2. Processes hollow for their whole 



length. 



