i68 TUFTS COLLEGE STUDIES, VOL. II, No. 3 



13. SCENEDESMUS Meyen, 1829, p. 774. 



Colonies free, of 2-8 cells, in one row, or in two rows side by 

 side ; ovoid or with pointed ends, all smooth or all or part with 

 spines or horns ; chromatophore nearly filling the cell, with one 

 pyrenoid ; division either by longitudinal walls through each 

 cell, or also by a wall through the length of a colony, dividing 

 each cell across the middle ; daughter cells escaping either 

 singly or united in colonies ; the free cells often differing con- 

 siderably in form from the normal colony cells. 



Common in gatherings of miscellaneous algae from still water; 

 in such collections made in warm weather one is almost certain 

 to find colonies of Sccnedesmus ; but it is unusual to find them 

 constituting the bulk of a collecting. 



KEY TO THE SPECIES OF SCENEDESMUS. 



i. Ends of cells obtuse or rounded. 2. 



i. Ends of cells acute. 2. S. obliquus. 



2. Terminal cells of series with long projections. 



5. S. qnadricauda. 



2. All cells similar. 3. 



3. Cells without teeth or spines. i. S. bijuga. 



3. Cells with teeth or spines. 4. 



4. Cells covered with minute spines. 4. S. Hystrix. 



4. Cells with denticulate ends. 3. S. dcnticulatus. 



1. S. BIJUGA (Turp.) Wittr., Nordst. and Lagerh., Alg. 

 Exsicc., No. 1567; P. B.-A., No. 1220; .S". obtusus Wolle, 

 1887, p. 173, PI. Civ VI, figs. 22-24. Colonies of 4-8 cells; cells 

 oblong-ellipsoid or ovoid, with rounded ends, 7-18X4-7 p-, 

 arranged in a single or double row. Greenland, Me., Mass., 

 Neb., Cal. Europe. 



Var. ALTERNANS (Reinsch) Hansgirg, 1886, p. 114; P. 

 B.-A., No. 1181. Cells broader than in the type, in two rows, 

 alternately placed ; merely a form, hardly worthy of a name. 

 Porto Rico, Cal. E/trope. 



Var. flexuosus (L,emmermann) nov. comb. ; J?. bijitgatns var. 

 flexuosns L,emrnermann, 1898, p. 191, PI. V, fig. i ; Snow, 1903, 

 p. 375, PI. I, fig. IV. Cells 8-16-32 in a single series, io-2o> 

 5-8 ju. L,ake Erie. Europe. 



2. S. OBLIQUUS (Turp.) Kiitzing, 1833, p. 609; P. B.-A., 

 No. 1320; S.acutus Nageli, 1848, PI. V. A, fig. 3. Colonies of 

 4-8 cells, cells fusiform with acute ends, usually in a single 

 series, 5-27X3-9 /.. Fig. 53. Me., Mass., Neb., Barbados, 

 Cal. Europe. 



