1919] Setchell-Gardner : Myxophyceue 109 



4. Rivularia mamillata S. and G. 



Plate 6, fig. 19 



Tlialli 0.5-1 mm. diam., bright blue-green or brownish ; spherical 

 or irregular in outline, more or less confluent, forming congested, pul- 

 verulent layers, or scattered among other Myxophyceae ; filaments 

 repeatedly false branched, spreading widely above, separating onh- 

 under considerable pressure ; sheath hyaline below, yellowish brown 

 above, distinct below but very thin above, ocreate, trichomes tapering 

 gradually from the base upward, terminating in a long hyaline hair, 

 4-5/i, diam. at base; cells 2-5/a long, sliglitly torulose, blue-green, de- 

 cidedly granular; heterocysts spherical to bluntly conical, 5.5-8/i, diam. 



Growing on decaying logs along high-tide level in somewhat shaded 

 localities. Cape Flattery, Washington. 



Setchell and Gardner, in Gardner, New Pac. Coast Alg. Ill, 1918a, 

 p. 475, pi. 40, fig. 19. 



This species closely resembles R. nitida Ag. but has more distinct, 

 ocreate sheaths, larger trichomes with shorter cells, and a less ample 

 thallus. 



FAMILY 6. STIGONEMATACEAE kirchner 



Filaments free, or forming a pannose or pulvinate stratum, or 

 united into definite, more or less gelatinous colonies, composed of a 

 single series of cells or of two or more series within a sheath, resulting 

 from cell divisions in two or more planes ; branches connately joined 

 or in some genera both true and false branches; cells cylindrical, 

 subspherical, or irregularly angular; heterocysts intercalary or term- 

 inal on short lateral branches; multiplication by hormogonia and b}- 

 resting spores. 



Kirchner, m Engler and Prantl, Natiirl. Pflanzenfam. T, Tli. 1, 

 la Abt., 1898, p. 80. Stigonemeae Hassall, Brit. F. AV. Alg., vol. 1, 

 1845 (also editions of 1852 and 1857), p. 227. Sirosiphoniaceae Raben- 

 horst, Fl. Eur. Alg., vol. 2, 1865, p. 2; Bornet and Flaluiult, Rev. 

 Ill, 1887, p. 51. Stigonemaceae Forti, in De-Toni, Syll. Alg., vol. 5, 

 1907, p. 562. 



Bornet and Flahault (1887, p. 51) use the name Sirosiphoniaceae 

 of Rabenhorst (1865, p. 2), but Sirosiphon has been dropped from 

 the list of valid genera. It seems necessary to reject the name (ef. 

 Art. 52, Regl. Intern de la Nom. Bot., 1906) and to adopt Ha-ssall's 

 name of 1845 (p. 227) giving it the form adopted by Forti. This form 



