THE GREEN ALGAE OF NORTH AMERICA 171 



which often remain attached by the general gelatinous envelop, 

 forming a rectangular plate, which may measure as much as 

 150 fj. on a side, and in which the number of cells is normally 

 some power of four. Lake Erie. Europe. 



15. SELENASTRUM Reinsch, 1867, p. 64. 

 Cells crescent or sickle-shaped, with parietal chromatophore 

 and no pyrenoid ; usually united in families of 4-8-16 ; asexual 

 reproduction by division of cell into 4 daughter cells, which 

 arrange themselves like the parent. 



KEY TO THE SPECIES OF SEI.ENASTRUM. 



i. Cells less than 10 /j. from tip to tip. i. 5. minututn. 



i. Cells 16 fj. or more from tip to tip. 2. S. Bibraianutn. 



1. S. MINUTUM (Nag.) Collins, P. B.-A., No. 1422; Raph- 

 idium mimttum Nageli, 1848, p. 82, PI. IV.C, fig. 2. Cells 

 crescent-shaped, usually uniformly curved ; 7-9 p, from tip to 

 tip to tip, 2-3 p. wide at middle ; cells rarely continuing united, 

 usually free. Fig. 55. Mass. Europe. 



2. S. BIBRAIANUM Reinsch, 1867, p. 64, PI. IV, fig. 2 ; P. 

 B.-A., No. 1317. Cells crescent- or sickle-shaped, uniformly 

 curved or with tips straight ; families of four cells joined at the 

 middle of the convex side of each cell ; these four-celled families 

 often united in subspherical colonies of 8 or 1 6 cells ; cells 

 16-23 p. long, 5-8 p. wide at thickest part. Me., Mass., Wash. 



Europe. 

 16. KIRCHNERIELLA Schmidle, 1893, p. 83. 



Cells arcuate or crescent-shaped, uninucleate, with parietal 

 chromatophore and usually one pyrenoid, loosely aggregated 

 without apparent order in a large gelatinous mass ; asexual re- 

 production by division into 4 or 8 daughter cells. 



K. LUNARIS (Kirchner) Moebius, 1894, p. 331 ; Chodat, 1902, 

 p. 202, figs. 121 and 122. Cells crescent- shaped, with rounded 

 ends, 3-5 /x diam. at middle, 6-10 /u, long. Fig. 56. Me., Mass. 



Europe. 



Var. DIANAE Bohlin, 1897, p. 20, Pi. I, figs. 28-30; P. B.-A., 

 No. 1513. Cells more curved, tips acute and often not in the 

 same plane. Me., Mass. So. America. 



The 'genus differs from Sclenastrum by the absence of any 

 definite arrangement of the individual cells, and by the presence 

 of an ample enclosing mass of gelatine. Both type and variety 

 of K. lunaris occur among water plants in ponds, etc. 



17. COE^ASTRUM Nageli in Kiitzing, 1849, p. 195. 



Cells spherical to polygonal, uninucleate, with bell-shaped 



