Selenastrum gracile Reinsch 1867, p. 65 



PI. 57, Fig. 11 



Colonies of 8-64 sickle-shaped cells in irregular arrangement, but 



with the convex surfaces apposed; apices of the cells sharply 



pointed; chloroplast a parietal plate along the convex wall, without 



a pyrenoid (?); cells 3-5/a in diameter, 19-28^ between apices. 



In tychoplankton of lakes and swamps. Mich., Wis. 



Selenastrum minutum (Naeg. ) Collins 1909, p. 171 

 PI. 46, Fig. 10 



Cells often solitary or in small famihes, irregularly arranged, 

 crescent-shaped, the poles bluntly pointed; cells 2-3/a in diameter, 

 7-9/x between apices. 



Mich. 



Selenastrum Westii G. M. Smith 1920, p. 133 



PI. 57, Fig. 10 



Colony small, composed of 2-8 slender, lunate or arcuate (but 

 not sickle-shaped) cells, arranged with their convex walls apposed; 

 chloroplast a parietal plate lying along the convex wall; pyrenoid 

 lacking (?); cells 1.5-2.5;^ in diameter; 15-18/a between apices. 



Rare; in euplankton. Mich., Wis. 



KIRCHNERIELLA Schmidle 1893, p. 83 



Free-floating or caught among larger algae; a colony of strongly 

 curved, lunate, sickle-shaped or twisted fusiform, sometimes cylin- 

 drical cells, inclosed by a gelatinous envelope in which there is 

 no regular arrangement of individuals although young colonies may 

 have even numbers of individuals, and these are usually arranged 

 so that the convex walls are together; chloroplast a parietal plate 

 along the convex wall, with 1 pyrenoid. 



Key to the Species 



1. Cells inclosed by the persistent mother cell 



wall of the last generation K. subsolitaria 



1. Cells inclosed by a copious mucilaginous sheath _ 2 



2. Cells vermiform cylinders, rounded at the poles 3 



2. Cells lunate, sickle-shaped, sharply or bluntly pointed at the apices 4 



3. Cells small, 2/^ or less in diameter, up to 14^ long K. contorta 



3. Cells larger, 2-3|U in diameter, up to 



25m long; spirally twisted K. elongata 



4. Cells narrowed at the poles, rounded or bluntly pointed K. obesa 



4, Cells sharply pointed at the poles K. lunaris 



[257] 



