Key to the Species 



1. Cells oblong or subquadrate; the lateral walls unsymmetrical 



because of longitudinal folds .._ _ G. crenulatocollis 



1. Cells ovate, spheroidal, or oblong to subcylindrical; wall 



without folds, the cells symmetrical 2 



2. Cells adjoined to form continuous filaments G. minor 



2. Cells not adjoined, separated from one another 



within a gelatinous sheath 3 



3. Cells in linear pairs, pairs separated from neighboring pairs 



by a cell's length; cell 5-8/^ in diameter G. interrupta 



3. Cells not in pairs; evenly spaced in a linear series 4 



4. Cells separated from one another by a cell's length or more G. ordinata 



4. Cells separated from one another by less than a cell's length G. mutabilis 



Geminella crenulatocollis Prescott 1944, p. 349 

 PI. 6, Figs. 9, 10 



Uniseriate filaments of irregularly ovoid, subquadrate, or oblong 

 cells, with emarginate, crenulate, or wavy lateral walls; truncate or 

 broadly rounded at the poles, with folds and ridges sometimes pres- 

 ent in the lateral walls. Cells inclosed by a broad gelatinous sheath 

 and arranged in linear pairs, but often evenly spaced. Chloroplast 

 an irregularly shaped, folded parietal plate, which makes an almost 

 complete cylinder within the wall, often showing a ridge or wing- 

 like flange extending radially toward the wall. Cells 12-15/i, in 

 diameter, 18-24/x long. 



This species should be compared with G. mutabilis, from which 

 it difiFers in the irregularly creased cell wall and the shape of the 

 chloroplast. Originally described from Wisconsin, this species has 

 since been found in Michigan. 



In soft water and acid swamps; tychoplanktonic in mixtures of 

 algae in lake margins; in Sphagnum bogs. Mich., Wis. 



Geminella interrupta (Turp.) Lagerheim 1883, p. 68 



PL 6, Fig. 15 

 Uniseriate filaments of broadly ovoid or subcylindric cells; pairs oi 

 cells separated from the next pair in the series by at least a cell's 

 length. Cells 5-8|U in diameter, 6-15fi long. Chloroplast a parietal 

 plate covering % of the cell wall. 



This species, even more than others in the genus, seems to be 

 confined to soft water lakes. It appears in great profusion in desmid 

 habitats. Mich., Wis. 



Geminella minor ( Naeg. ) Heering 1914, p. 41 

 PI. 6, Fig. 17 

 Uniseriate filaments of short, cylindrical cells adjoined without 

 interruption within a wide gelatinous, homogeneous sheath. Chloro- 



[100] 



