THE GREEN ALGAE OF NORTH AMERICA 183 



10. Cells 15-20 /j. diam. 4. U. tenuissima. 



10. Cell ii M diam. 5. U. osdllarina. 



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

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

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

 Filaments 5-6 //. diam., cells cylindrical, ^-i^ diam. 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. snbtilis 

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

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

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

 5-8 fj. 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, PI. IX, fig. i ; 

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

 No. 1468. U. snbtilis var. tenerrima Wolle, 1887, p. 136, PI. 

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

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

 y$-\yi 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, 18333, p. 518; Hazen, 1902, p. 

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

 dark green, 15-20 p., rarely 25 /* diam.; cells cylindrical, except 

 when fruiting, about }4 diam. long; chromatophore a broad 

 band. 



