STAURASTRUM. 121 



4 



SECTION E. Cells furnished with spines at the angles only, each 

 angle provided with single or binate spines, rarely with three or 

 four. 



About 29 species. 



SECTION F. Cells with numerous spines, either clothing the 

 whole surface of the cell-wall or more or less restricted to the 

 vicinity of the angles. 



v O 



About 21 species. 



SECTION G-. Cells with verrucse, which are emarginate or very 

 much reduced and 2-3-spinate. 



About 8 species. 



Division II. Angles of semicells produced into processes. 



a. Processes arising exclusively from the angles of the semicells, 

 and therefore ail arising in the same horizontal plane. 



SECTION H. ' Processes smooth (although usually emarginate, 



O / 



furcate, or spinate at the extremity). 



About 9 species. 



SECTION I. Processes rough, denticulate or spiiiate along their 

 whole length. 



About 46 species. 



b. Processes not arising exclusively from the angles of the semi- 

 cells, and therefore with their points of origin in more than one 

 horizontal plane. 



SECTION J. Semicells with accessory processes, most commonly 

 of dorsal origin. 



O 



About 15 species. 



The ten sections just enumerated not only meet all the require- 

 ments of the British species, but of all the known species of 

 Staurastrum. We have indicated, in most cases provisionally, the 

 number of British species of each section. 



In most of these sections there are species of an intermediate 

 character of which the exact systematic position is somewhat doubt- 

 ful. To the best of our judgment we have placed these species 

 alongside their nearest relatives. 



For greater convenience, a synopsis of the British species con- 

 tained in any section is given immediately in front of that section. 



