On Platydorina. 437 



Cells not connected by protoplasmic processes, of 

 two sizes, smaller vegetative at anterior pole and 

 6 <[ larger gonidial at posterior. Pleodorina. 



Cells connected by protoplasmic processes, not mark- 

 edly different in size. Volvox. 



Species. 



Gonium. 



f Cells, 4. sociale (Duj.).t 



\ Cells, 16. pectorale Mull. 



Stephanosphsera. 



Kepresented by a single species, characterized as follows : 

 Cells 4 or 8, ovoid or spindle-shaped, with numerous pro- 

 cesses, pluvialis Colin.* 



Pandorina. 



Eepresented by a single species, characterized as follows : 

 Cells 16 or 32, crowded, each with a single chromatophore 

 and pyrenoid. morum Bory. 



Eudorina. 



Eepresented by a single species, characterized as follows : 

 Cells 32, 16, or 64, similar, not crowded together, common 

 outer membrane without marked concentric structure. 



elegans Ehrb. 

 Platydorina. 



Kepresented by a single species, characterized as follows : 

 Cells 16 or 32, arranged in a horse-shoe-shaped plate, 

 those of the two faces intercalated. Posterior end with 3 

 or 5 tails. caudata Kofoid. 



Pleodorina. 



Cells 64 or 128 ; gonidial cells about 2-3 times the diam- 

 eter of vegetative cells, which constitute about one half 

 the total number and lie in anterior hemisphere. 



calif orn ica Shaw. 



Cells 32, rarely 16 or 64; gonidial cells not more than 

 twice the diameter of the vegetative cells, which con- 

 stitute the anterior quartet. illinoisensis Kofoid. 



