Myxo 95 



species resemble very much those of Microcoleus subtorulosus, 

 but the exterior aspect of the two plants is totally different. 



l88. Phormidium luridum (Kuetzing) Gomont. Monogr. Oscill. 185. pi. 4. 

 f. 17, 18. 1893. De Toni. Syll. Algar. g: 222. 1907. 

 West and West. A further Contribution to the Freshwater Algae of the 

 West Indies. Journ. Linn. Soc. Bot. 34: 289. 1898-1900. West. West In- 

 dian Fresh Water Algae. Journ. of Bot. 42: 292. 1904. 



Plate IV. fig. 56, 57. 



Plant mass membranaceous, lamellose, amethyst-purple or dark purple 

 en the surface, gray or blue-green underneath; filaments somewhat straight; 

 sheaths at first thin, scarcely visible, soon dissolving into a compact, gelat- 

 inous mucus; trichomes 1.7-2 mic. in diameter, fragile, straight, variously 

 entangled, slightly constricted at joints; apex of trichome neither curved 

 nor tapering; apical cell rotund; calyptra none; cells 1.8-4.7 niic. in length; 

 cell contents not granular. 



West Indies. Growing on sides of road. Fort Charlotte, St. Vincent. 

 January and February 1896. (West). Roseau Valley, Dominica. (Howard). 



189. Phormidium rubrum Tilden. American Algae. Cent. II. no. 186. 1896. 

 Observations on some West American Thermal Algae. Bot. Gaz. 

 25: 100. pi. 9. f. 18. 1898. De Toni. Syll. Algar. 5: 223. 1907. 



Plate IV. fig. 58. 



Plant mass forming a thin layer, scarlet in color; filaments somewhat 

 straight; sheaths visible only under high powers; trichomes i mic. in 

 diameter, fragile, frequently interrupted, not constricted at joints; apex 

 of trichome neither curved nor tapering; cells 1-1.2 mic. in length; trans- 

 verse walls rarely visible. 



Wyoming. In tepid water, in overflow from small hillside spring. Be- 

 tween Middle and Upper Geyser Basins, Yellowstone National Park. July 

 1896. (Tilden). 



190. Phormidium purpurascens (Kuetzing) Gomont. Essai Class. Nostoca- 

 cees homocystees. Morot. Journ. de Bot. 4: 3SS- 1890; Monogr. 

 Oscill. 186. pi. 4. f. 19. 1893. De Toni. Syll. Algar. 5: 223. 1907. 



Plate IV. fig. 59- 



Plant mass compact, leathery, dark violet; filaments strongly twisted, 

 closely entangled; sheaths narrow, papery, finally becoming diffluent and 

 agglutinated; triohomes 1.5-2.5 mic. in diameter, not constricted at joints; 

 apex of trichome neither tapering nor curved; apical cell rotund; calyptra 

 none; cells 2-4.5 mic. in length; transverse walls marked by four protoplas- 

 mic granules. 



Wyoming. Together with Synechococcus aeruginosusand 

 Gloeocapsa violacea, forming black -'stalactites," 1.-1.5 dm. long 

 and 5 dm in thickness, also serrated masses or extended sheets. These 

 hung from the top and lined the walls of a small cave in which was the 

 vent of a hot spring. At short intervals they received jets of steam and 



