THE GREEN ALGAE OF NORTH AMERICA' 41 



KEY TO THE SPECIES OK E^AKATOTHRIX. 

 i. Sheath little or not branched ; cells narrowly fusiform. 



1. E. gelatinosa. 

 i. Sheath branching and anastomosing ; cells broad fusiform or ovoid. 



2. E. americana. 



1. E. GELATINOSA Wille, 1898, p. 302; Pascher, 1915, p. 

 220, figs. 25 & 26. Cells elongate fusiform, 18-22 X 4-6 /*, in 

 more or less distinct linear series ; gelatinous sheath cylindrical 

 or subfusiform, little or not at all branched, containing up to 

 32 cells, rarely more. Fig. 14. Wis., G. M. Smith. 



Northern Europe. 



2. E. AMERICANA Wille, 1899, p. 150; P. B.-A., No. 607. 

 Cells broad fusiform or ovoid, 12-25 X 6-15/1; gelatinous 

 sheath in the form of a laciniate, anastomosing thallus, attached 

 to various plants and reaching a length of several cm. ; later 

 forming floating masses of indefinite form. Conn. 



Northern Europe. 

 FUSOLA Snow, 1903, p. 389. 



Cells fusiform, parietal chromatophore nearly or quite cover- 

 ing the wall, with large central pyrenoid ; asexual reproduction 

 by transverse division of cell, the daughter cells separating and 

 issuing from the mother cell ; single cells surrounded by a 

 broad gelatinous coating of similar shape to the cell, containing 

 2-4 daughter cells during division, then dividing to contain a 

 single cell. Only one species. 



F. VIRIDIS Snow, 1903, p. 389, PI. II, fig. 6 ; Elakatothrix 

 americana Collins, 1909, fig. 51, not of p. 167. Cells 27-40 X 

 9-12 /A, broad fusiform, sometimes slightly sigmoid ; sheath 

 35-60X15-25/4. Lake Erie. Northern Europe. 



Pascher, 1915, p. 220, gives Fusola americana Snow as a syno- 

 nym of Elakatothrix americana ; no such binomial was used. 



Page 1 68, after generic description of SCENEDESMUS, cancel 

 key, and substitute, 



A very thorough monograph of this genus, G. M. Smith, 

 I9i6a, has been utilized for the following account of the American 

 forms. These are now given in the same order and under the 

 same names as in the monograph, with descriptions of all not 

 already described in this work. 



KEY TO THE SPECIES OF SCENEDESMUS. 

 i. Cell membrane smooth, without terminal spines, teeth, granulations 



or lateral ridges. 2. 



i. Cells with projections of some sort. 8. 



2. Cells acicular to fusiform. 3. 



2. Cells ovoid. 7- 



