Myxophyceae 139 



3 Plant mass forming a small mat; filaments 1.5-2 mic. in diameter; 



sheaths closely adherent, entirely diffluent H. gloeophila 



4 Plant mass thin, cushion-shaped, mucous; filaments 1.8-2.2 mic. in 



diameter; sheaths close H. herbacea 



5 Plant mass sometimes expanded, forming loosely interwoven masses 



or small cushion-shaped clusters; filaments 3.5-4 mic. in diameter; 

 sheaths firm, close H. tenax 



6 Plant mass somewhat spherical, hollow, tough, yellowish or light 



straw-colored; filaments 4-6 mic. in diameter; trichomes 1.5-2 

 mic. in diameter H. bullosa 



7 Plant mass compact, leathery, brick-colored; filaments up to 7.5 



mic. in diameter; sheaths wide, membranaceous, firm, homogeneous, 

 smooth; trichomes 3.2-4 mic. in diameter, here and there inter- 

 rupted H. turicensis 



8 Plant mass more or less expanded, olive green; filaments 8-1 1 mic. 



in diameter; sheaths moderately wide; trichomes 3.5 mic. in diame- 

 ter, here and there interrupted, often constricted at joints 



H. aikensis 



II Filaments long and flexible, disentangled without rupturing 



1 Plant mass encrusted with calcium carbonate; trichomes 1-1.7 mic. 



in diameter; cells longer than the diameter H. coriacea 



2 Plant mass not encrusted with calcium carbonate; trichomes 1.5-2 



mic. in diameter; cells longer than the diameter 



H. lardacea 



3 Plant mass not encrusted with calcium carbonate; trichomes 1.5-3 



mic. in diameter; cells longer than the diameter 



H. arenaria 



4 Plant mass compact, leathery, roughened; trichomes 2.3-2.8 mic. in 



diameter; cells a little shorter than the diameter 



H. vulpina 



5 Plant mass membranaceous, firm, smooth, pale rose or dark red; 



trichomes 5.6-8.3 mic. in diameter; cells somewhat quadrate 



H. pallida 



266. Hypheothrix calcicola (Agardh) Rabenhorst. Fl. Eur. Algar. 2: 78. 

 1865. Gomont. Monogr. Oscill. 45- pl- 8. f. 1-3. 1893. (S c h i z o- 

 thrix calcicola Gom.). De Toni. Syll. Algar. 5: 327. 1907. 



Anderson and Kelsey. Common and conspicuous Algae of Montana. 

 Bull. Torr. Bot. Club. 18: 145. 1891. (Leptothrix calcicola Kg.). 

 Saunders. Protophyta-Phycophyta. Flora of Nebraska. 21. pl. 2. f. 19. 1894 

 Tilden. American Algae. Cent. II. no. i8o. 1896; (P. purpurascens 

 (Kuetz.) Gom.); On some Algal Stalactites of the Yellowstone National 

 Park. Bot. Gaz. 24: 197. pl. 8. f. 3, 4. 1897; Observations on some West 

 American Thermal Algae. Bot. Gaz. 25: 98. 1898. Collins, Holden and 

 Setchcll. Phyc. Bor.-Am. Fasc. 12. no. 557. 1899. 



