GENERA OF ALGVE. 2^ 



b. Aerial, on moist objects; gelatinous, cells globose or angular, be- 



coming red .... . Porphyridium, 57 



c. Family in jelly mass, thallus pyriform, irregular, tubular, clustered, 



branched, etc. (/). 

 c. Family globose {d). 



c. Family plane, discoid or stellate, often perforated; cells polygonal, 



Pediastrum, 40 

 c. Family cubical, cells 4-8-16, rhomboidal . . Staurogenia, 44 



c. Family of laterally united, often spinous or crescentic cells (e). 



c. Family of cylindrical cells (/). 



d. Cells in a single stratum; ccenobium hollow . . Cxlastrum, 42 

 d. Cells 4-8-16-32, wedge-shaped, apices sinuate or bifid; ccenobium 



solid Sorastrum, 43 



d. Cells 2-4-8, globose or oblong . . Glmocystis, 60 



e. Cells cylindrical to ovate, ends often spinous . Scenedesmus, 45 

 e. Cells not spinous, fusiform, cylindrical, straight or variously curv- 

 ed, single or united .... .... Rhaphidium, 62 



/. Upper cells spreading, contracted at base . . . Sciadium, 46 



g. Cells globose or pear-shaped (h). 



h. Neck not cylindrical, aperture with a lid . Ckytridium, 68 



h. Neck cylindrical, elongated . Olpidium, 69 



i. Cells connected by fine filaments (*). 

 /. Cells not connected by filaments (7). 



* Filament attached to the convex side of the cells, 



Dimorphococcus, 63 



* Filament attached to the concave side of the cells, 



Dictyospharium, 51 

 j. Families free-swimmirig (not attached), (k). 

 j. Families not free-swimming (attached), (/). 

 k. Cells oblong, reniform, 2-4-8-16; tegument oval or reniform; 



variable ... Nephrocytium, 61 



k. Cells oval, small, in grape-like clusters; tegument thin, diffluent, 



Botrycoccus, 59 

 k. Cells globose, large, cell walls firm, border hyaline; chlorophyll 



sometimes radiate . . . .... Eremosphcera, 65 



/. Cells fusiform, crescentic or straight, cylindrical, ends cuspidate or 



acuminate, tegument thin . ... Rhaphidium, 62 



/. Cells globose, elliptical or elongate (m). 

 m. Cells red, large; tegument thick, concentrically lamellate, stem 



ringed . ... Urococcus, 66 



m. Cells green; tegument not lamellate («). 



