220 FRESH-WATER ALG^ OF THE UNITED STATES. 



S. jugalis and S. setiformis appear closely related, probably 

 ought to be united; following the example of Mons. Petit 

 their separate positions are retained. The one having some- 

 what inflated fruit-bearing cells, the other not, they differ 

 also in some degree in the form of the zygospores. 



Common in ponds and quiet river waters. 



Syn. Conferva setiformis^ Both ; Zygnema interruptum, Hass. 



Plate CXXXYIII, fig. 1, sterile filament ; fig. 2, fruiting 

 filament approaching maturity, showing the spirals of the 

 coming germs in the zygospores ; figs. 3, 4, two spores 

 germinating. 



SPIROGYRA DUBIA, Kg. 



Diameter of vegetative filaments, 43-50 yu ; cells li-2* 

 times as long as broad; chlorophyl bands two, or more 

 rarely three, narrow, nodose, lax, making each 1-2 turns in 

 a cell ; sporiferous cells slightly swollen. Zygospores oval- 

 elliptic, or subcylindrical, as broad as long, or one-half 

 longer. 



Ditches; fruiting abundantly in May; forming dirty, 

 light yellowish-green masses. 



Var. LONGI-ARTICULATA, Kg. 



Cells five times as long as broad, spirals 2 or 3 ; turns in 

 cell, 7-8. 



Plate CXXXV, figs. 11, 12, typical form, sterile and 

 fertile filaments. 



SPIROGYRA ADNATA, Kg. 



Diameter of vegetative cells, 40-45 ^ ; cells 1-3 times as 

 long as broad ; 2, sometimes 3, spirals, making 3-4 turns 

 each ; spore-bearing cells moderately swollen ; zygospores 

 oval-elliptical. 



Stagnant waters, New York, Iowa. 



Syn. Zygnema adnatum, Ag. ; Conjugata adnata, Yauch. 

 Plate CXXY, figs. 3, 4, sterile and fertile filaments. 



Appears nearly related to /S. decimina, but vegetative cells 

 are shorter and spore-bearing cells are more or less inflated. 



SPIROGYRA RIVULARIS, Eab. 



Diameter of vegetative filaments, 32-36 ^ ; cells of sterile 

 plants 7-11 times as long as wide. Fertile cells usually 

 about four times longer than wide ; cylindrical or slightly 

 tumid. Three spirals (rarely 2 or 4), lax, making 2- 

 turns in a cell. Zygospores oval-elliptical. 



