THE GREEN ALGAE OF NORTH AMERICA 183 



10. Cells 15-20 //. diatn. 4. U. tenuissima. 



10. Cell ii /x cliam. 5. U. oscillarina. 



1. U. VARIABILIS Kiitzing, 1849, p. 346; Hazen, 1902, p. 

 152, PI. XXI, figs. 5-7 ; P. B.-A., Nos. 1022, 1373 ; ? U. subtilis 

 var. variabilis Wolle, 1887, p. 136, PL CXVIII, figs. 15-16. 

 Filaments 5-6 //. diam., cells cylindrical, ^2-1 ^ diani. long, wall 

 very thin and delicate ; chromatophore usually occupying about 

 half the cell wall, often quite irregular in shape and position ; 

 pyrenoid single, small. Europe. 



This species forms floccose masses in brooks and quiet waters. 

 It has been reported from Greenland, a few localities in the- 

 eastern States, from Trinidad, and from California. 



2. U. caldaria (Kiitz.) nov. comb. ; Gloeotila caldaria Kiitz- 

 ing, 1849, p. 363.; 1853, p. 10, PI. XXXII, fig. 3; U. subtilis 

 var. thermarum Wolle, 1887, p. 136, PL CXVIII, figs. 18 and 

 19; Hormiscia flaccida var. caldaria Tilden, Amer. Algae, No. 

 130. Filaments soft and mucilaginous, bright or dull green, 

 5-8 p- diam., cells 1-3 diam. long, cylindrical; chromatophore 

 (in dried specimens) apparently occupying the entire cell wall. 

 Forming long strings and floccose masses in warm or hot water. 

 Yellowstone Park ; Pa. Europe. 



Our only distinctly thermal species. 



3. U. TENERRIMA Kiitzing, 1843, p. 253, PL IX, fig. i ; 

 Hazen, 1902, p. 151, PL XXI, figs. 3 and 4; P. B.-A., 

 No. 1468. U. subiilis var. tenerrima Wolle, 1887, p. 136, PL 

 CXVIII, fig. 17. Forming light green silky masses, often of 

 considerable length; filaments 7-9 /x diam.; cells cylindrical, 

 J/3 -i J/3 diam. long; wall very thin; chromatophore zonate, or 

 contracted to one side of the cell ; pyrenoid single. Vt, Mass., 

 Cal. Europe. 



The single pyrenoid seems to distinguish this species from all 

 others except U. variabilis ; these two species are certainly 

 quite near each other, but U. tenerrima is a larger species, with 

 the chromatophore more fully and regularly developed. The 

 material from California distributed "as P. B.-A., No. 1468, is in 

 the Gloeocystis state, and its connection with this species 

 though probable is not certain. 



4. U. TENUISSIMA Kiitzing, i833a, p. 518; Hazen, 1902, p. 

 149, PL XX, figs. 5 and 6; P. B.-A., No. 1021. Filaments 

 dark green, 15-20^, rarely 25 /xdiam.; cells cylindrical, except 

 when fruiting, about ^ diam. long; chromatophore a broad 

 band. 



