22 DESMID- OF THE UNIIED STATES. 



Crtnus, GOXATOZYGOX. D. Bj-. 

 Cells long, cylindrical, or truncate spindle form, without con- 

 striction, united into fragile, filiform straight series ; at maturity 

 they separate and become geniculate, copulate and produce spher- 

 ical zygospores : these separate quickly from the empty cells. 

 Two species only have been recognized in this country. 



G. ASPEEUM. (Ealfs) Eab. Probably identical with G. Ealfsii, 

 De By. Plate I, fig. 1. 



Cells long, cylindrical, ten to twenty times as long as wide, 

 very slightly, or not at all reduced in thickness at the ends. 

 Cytioderm fine-granularly roughened. 

 Diameter 11-12 yw. 



Occurs frequently in ponds of Xew Jersey. 



G. PILOSA.M. WoUe. Plate I, fig. 2. 



Cells twelve to twenty times as long as wide, loosely con- 

 nected : cytioderm more or less densely clothed with .small, 

 straight hairlike spines ; cells cylindrical, terminal one of a 

 filament slightly attenuated, end rounded. 

 Diameter 15 ju. : with spines 25 //. 

 Habitat the same as the preceding. 



Geium, HYALOTHECA, Ehrb. 

 Plate I, figs. 3-14. 

 Cells .short, cylindrical, usually with a slight obtuse constric- 

 tion in the middle; disciform in end view, closely united into 

 long filaments, which are inclosed, each in an ample, colorless 

 mucous sheath. Chlorophyl mass in each cell, end view, six to 

 ten radiate. 



H. DissiLiEXS, (Smith) Breb. Plate I. figs. 3. 4. 5. 



Filaments elongated, cells slightly contracted in the middle, 

 usually about half as long as broad. Variable in size. 

 Diameter 20-36 /j. 



Yar. HiA>-s. Wolle. Plate XII, tigs. 14-16. 



Differs from the typical form in having the lateral margins 

 of the cells arched with an acute notch in the middle. 

 Diameter 2.5-50 //. 



Biidd's Lake, N. .7., and Florida. 



Frequent in ponds and sluggish, shallow waters. The fre- 

 quency of this plant soon familiarizes it ; usually It is found 

 intermingled with other forms, but sometimes it has entire 



