THE GREEN ALGAE OF NORTH AMERICA 193 



1. M. CRASSIOR (Hansg.) Hazen, 1902, p. 169, PI. XXIII, fig. 

 2; P. B.-A., No. 1070; M. amocna forma crassior Wille, 1899, 

 p. 149. Filaments long, dark green, nearly cylindrical, 28-33 /* 

 diam., cells 1-1.6 diam. long, with wall 2.5-3 M thick ; lamellate 

 structure usually distinct ; chromatophore dense, covering the 

 whole cell wall and hiding the large nucleus. 



The largest species of the genus, the nearest species, M. 

 amocna, being considerably smaller, with thinner walls and rela- 

 tively shorter cells. It forms thick tangled masses in rapid 

 brooks, from May to October. Mass, to N. Y. Europe. 



2. M. AMOENA (Kiitz.) Rabenhorst, 1868, p. 321 ; P. B.-A., 

 No. igb as Ulothrix zonata, No. 616 ; Hazen, 1902, p. 170, PI. 

 XXIII, fig. i ; Conferva amocna Wolle, 1887, p. 140, PI. CXXI, 

 figs 1-5. Filaments long, dark or bright green, nearly cylindri- 

 cal, 21-25 P- diam-; cells 1-2 diam. long, with wall about 2 /A 

 thick ; chromatophore dense, covering the whole cell wall, and 

 hiding the quite large nucleus. In rapid brooks, forming more 

 or less tangled, often quite long masses, April to July. Mass, 

 to N. J. Europe. 



3. M. LOEFGRENII (Nordst.) Lagerheim, 18873, p. 417 ; 

 Hazen, 1902, p. 171, PI. XXIII, figs. 3 and 4; Wittr. and 

 Nordst., Alg. Exsicc., No. 17. Filaments long, 16-20 //. diarn., 

 cells distinctly swollen, 1-2 diam. long, wall about 2.5 /x thick ; 

 chromatophore dense, covering the whole cell wall, concealing 

 the nucleus. N. Y., Mass. Europe, So. America. 



Smaller than M. amoena, and with distinctly swollen cells ; 

 but otherwise of the same character as that species and M. cras- 

 sior. 



4. M. PACHYDERMA (Wille) Lagerheim, 18873, p. 415; 

 Conferva pachyderma Wille, 1881, p. 13, PI. IX, figs. 28-35. 

 Filaments 8-14 -p. diam., cells 1^-3 diam. long, wall up to 3 /*. 

 thick ; akinetes rounded-quadrate to ellipsoid, not larger than 

 the vegetative cells. Greenland. Europe. 



5. M. WITTROCKII (Wille) Lagerheim, 18873, p. 417 ; 

 Hazen, 1902, p. 172, PI. XXIII, figs. 5-7; Wittr. and Nordst., 

 Alg. Exsicc., No. 422. Filaments long, silky, light green, per- 

 fectly cylindrical, about 20 //. diam.; cells 1-2^ diam. long, wall 

 about 1.5 /i thick, not distinctly lamellate; chromatophore thin, 

 often perforated, or not occupying the full length of the cell, the 

 large nucleus usually quite distinct. Vermont, Mass., N. Y. 



Europe. 



A more delicate plant than any of the preceding species and 

 apparently common in early spring, often in company with M. 

 stagnorum. 



