pectic compounds, usually deposited in layers. Zygospores formed 

 in the enlarged conjugating tube, compressed-spheroid or quadrate 

 in front view, the median spore wall smooth or variously sculptured 

 and decorated, brownish in color. 



This genus should be compared with Zijgnema, especially those 

 species which have stellate chloroplasts. It is separated from that 

 genus chiefly by the presence of swollen and filled gametangia. 



Key to the Species 



1. Vegetative cells 16-22/n in diameter 2 



1. Vegetative cells smaller 3 



2. Zygospores ovate or quadrangular-ovate, 



median spore wall scrobiculate - Z. decussata 



2. Zygospores quadrate, outer wall densely punctate Z. spiralis 



3. Median and outer spore walls smooth 4 



3. Median or outer spore walls decorated __ 5 



4. Vegetative cells 8-10-( 12) /j. in diameter, with 



2 rounded chloroplasts Z. minuta 



4. Vegetative cells 10-12^ in diameter, with 



1 plate-like chloroplast .— Z. Tiffaniana 



5. Median spore wall finely reticulate; spores 20-40 jti in diameter, 



30-40;u long; 1 chloroplast with 2 pyrenoids Z. americana 



5. Median spore wall finely punctate; spores 14-24At in diameter, 



20-27/i long; 2 cushion-like chloroplasts in each cell Z. desmidioides 



Zygnemopsis americana (Trans.) Transeau in Transeau, 

 Tiffany, Taft, & Li 1934, p. 215 



Vegetative cells 9-12ytt in diameter, 27-120)Lt long; chloroplast with 

 2 pyrenoids. Zygospores formed in the tube but extending into the 

 gametangia; ovate or quadrangular-ovate in face view, the angles 

 retuse or rounded; median wall verrucose; 20-40/>t in diameter, 

 30-40/x long. 



Mich. 



Zygnemopsis decussata (Trans.) Transeau in Transeau, 

 Tiffany, Taft, & Li 1934, p. 214 



PI. 74, Fig. 3 



Vegetative cells 16-20/a in diameter, 24-50/a long; chloroplast with 

 2 pyrenoids. Zygospores irregular in shape, or ovate to quadrate- 

 ovate, somewhat compressed parallel with the conjugation tube; 

 the angles various, either rounded, retuse, or extended; median spore 

 wall scrobiculate; 24-30|U, in diameter, 30-48/a long, 



Mich. 



[327 ] 



