KEY TO THE GENERA OF THE DESMIDS. 



§ Cells united into filamefnts (a). 



§ Cells not united into filaments (g). 



a. In a transparent, jelly-like sheath (b'). 



a. Not in a jelly-like sheath {d'). 



b. Cells with 2 teeth on each narrow end Desmidium, 6 



b. Cells deeply constricted, almost into two parts (c). 



b. Cells not deeply constricted, and without teeth . . Hyalotheca, 3 



c. With 'claspers' across the sutures ... . Onychonema, 9 



c. Without 'claspers;' cells united by a narrow isthmus, Sphcsrozosma, 8 



d. Band not twisted; cells with 'claspers' across the sutures, 



Onychonema, 9 

 d. " " cells without 'claspers' (e). 



d. Band twisted; cells triangular or quadrangular . Desmidium, 6 



e. Cells barrel or hub-shaped, with i or 2 median bands, Bambusina, 4 

 e. " " " without bands, the sutures projecting, 



Leptozosma, 5 

 e. Cells cylindrical, sometimes swollen at base (/). 

 e. Cells quadrangular, deeply constricted, often slightly twisted, 



Phymatodocis, 7 

 /. Ten to 30 times longer than broad . Gonatozygon, i 



/. Three to 6 times longer than broad . . . Genicularia, 2 



g. Cell more or less crescentic . Closterium, 13 



g. Cell cylinilrical, fusiform, dumb-bell or hour-glass shaped (/). 

 g. Cell flattened; oiljiralar, oblong, or elliptical {K)'. 

 h. Mostly orbiculai- or broadly elliptical; centre deeply constricted, 

 the semi-celh 3-5 lobed, the lobes entire or variously incised, 



Micrasterias, 22 



h. Mostly oblong or elliptical; margins wavy, the depressions rounded; 



ends usually notched or incised ... . Euastrum, 21 



