THE GREEN ALGAE OF NORTH AMERICA 169 



Var. DIMORPHUS (Turp.) Hansgirg, 1886, p. 116; 6". acutus 

 var. dimorphus Rabenhorst, 1868. p. 64; 5". dimorphus P. B.-A., 

 Nos. 1020 and 1319. Cells united in a single series, end cells 

 crescent-shaped, median cells straight. Me., Mass., Neb., Cal. 



Europe. 



3. S. DENTICULATUS L,agerheim var. UNEARIS Hansgirg, 

 1886, p. 268. Colonies of 4-8 cells, in a nearly straight line, 

 4-5 ju, wide, to 15 n long ; each end with two minute teeth. 

 Greenland, Mass., Trinidad, Washington. Europe. 



The tj'pe with ovoid or oblong cells, 7-8X5-11 p, occurs in 

 Europe, but has not yet been reported from America. 



4. S. HYSTRIX Lagerheim, 1882, p. 62, PI. II, fig. 18. Col- 

 onies 2-8-celled ; cells oblong cylindric, straight with rounded 

 ends, in a single series, 12-18X3-6^; membrane with numer- 

 ous short spines. Porto Rico. Europe. 



5. S. OUADRICAUDA (Turp.) Brebisson, 1835, p. 66 ; Ralfs, 

 1848, p. 190, PI. XXXI, fig. 12 ; S. caudatus Wolle, 1887, p. 

 172, PI. CLVI, figs, ii and 12; P. B.-A., No. 1321. Colo- 

 nies of 2-8 cells, oblong-cylindric with rounded ends, 9-33X3-12 

 ju,, arranged in a single series or in two alternating rows ; end 

 cells usually with long, filiform projections ; intermediate cells 

 with rudimentary or no projections. Greenland, Me., N. H., 

 Mass., Ohio, Neb., Wyo., Jamaica. 



Europe, Asia, New Zealand. 



A very common species, the description above applying to the 

 typical form ; a number of varieties and forms have been de- 

 scribed, of which we have probably a good part ; the four fol- 

 lowing forms occur commonly : 



Forma TYPICUS Kirchner, 1878, p. 98. Projections on ter- 

 minal cells only. 



Forma SETOSUS Kirchner, 1878, p. 98. Projections on some 

 median cells. 



Forma HORRIDUS Kirchner, 1878, p. 98. Projections on all 

 cells. 



Forma ABUNDANS Kirchner, 1878, p. 98; Wittr. & Nordst., 

 Alg. Exsicc., No. 525. Terminal cells with median as well as 

 terminal projections. 



Var. ELiviPTicus W. &. G. S. West, iSgsa, p. 83, PI. V, fig. 



* Among the doubtful forms of the genus must be reckoned .S". rotunda- 

 tits Wood, 1872, p. 91 ; S. polymorphus Wood, 1872, p. 91; 5. antennatus 

 var. rectus Wolle, 1887. p. 172, PI. CLVI, figs. 16 and 17. 



