Dr. C. A. Kofoid on Platydorina. 557 



Species. 



Gonium. 



1 Cells 4 sociale (Duj.).t 



I Cells 16 perforate, MiilL 



STKPHANOSPHiERA. 



Represented by a single species, characterized as 

 follows : — Cells 4 or 8, ovoid or spindle-shaped, 

 with numerous processes pluvialis, Cohn.* 



Pandorina. 



Represented by a single species, characterized as 

 follows : — Cells 16 or 32, crowded, each with 

 a single chroraatophore and pyrenoid morum, Bory. 



EUDORINA. 



Represented 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. 



Represented by a single species, characterized as 

 follows : — Cells 16 or 32, arranged in a horse- 

 shoe-shaped plate, those of the two faces inter- 

 calated. Posterior end with 3 or 5 tails .... caudata, Kofoid. 



Pleoborina. 



f Cells 64 or 128 ; gonidial cells about two to three 



times the diameter of vegetative cells, which 



constitute about one half the total number 



•{ and lie in anterior hemisphere californica, Shaw. 



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



than twice the diameter of the vegetative 

 •__ cells, which constitute the anterior quartet. . illinoisensis, Kofoid. 



Volvox. 



f Cells about 10,000 (minimum 1-500, maximum 

 22,000), angular, with stout connecting 

 protoplasmic processes into which the chro- 

 matophore may enter. Diameter of colony 

 about 700 ft (minimum 400, maximum 



1200) ; diameter of cell-body 3-5 p glubator, L. 



Cells 500-1000 (minimum 200, maximum 4400), 

 rounded, with slender connecting protoplas- 

 mic processes into which the chromatophore 

 does not enter. Diameter of colony 170- 

 850 fj. ; diameter of cell-body 5-8 /x aureus, Ehrb. 



University of Illinois, 



Urbana, 111., U.S.A., 



Dec. 5, 1899. 



Ann. <& May. X. Hist. Ser. 7. Vol. vi. 37 



