106 University of Calif ornia Publications in Botany \yoh. 8 



and confusing. The first genus Rivularia was established by Roth in 

 1797 (p. 212). The two species assigned to it are both of the earlier 

 genus Chactophora Schrank (1783, p. 124). In 1800 (pp. 544-546), 

 Roth listed three species, all of the present Chactophora. In 1803 

 (pp. 261-285), however, Roth increased the genus as to the number 

 of species, adding some true Rivularias, and in 1806 (pp. 332-341) 

 he still further added to it additional Rivularia species as now 

 reckoned. In 1812 (p. 42) C. Agardh separat<?d the species of 

 Chactophora from the others and also refounded Rivularia {hoc. cit., 

 p. 43) in very nearly the sense in which we now use it. He repeated 

 his account later in 1817 (p. xxxviii) and even again in 1824 (p. 24). 

 The genus, then, had been refounded and well established even before 

 the Portaciis of Rafinesque (1819, p. 107) had been proposed. 



Key to the Species. 



1. Filaments separating from one another readily under pressure 



1. R. Biasolettiana (p 106) 



1. Filaments separating from one another with difficulty under pressure 2 



2. Fronds spherical or nearly so, at times more or less confluent into a layer.... 3 



2. Fronds globose to plicate-corrugate, expanded, often hollow 



3. R. nitida (p 108) 



3. Fronds spherical or irregular, 5-1 . mm. in diam., often gregarious and partially 



confluent into a pulverulent layer 4. R. mamillata (p 109) 



3. Fronds spherical or hemispherical, 3-5 mm. in diam., confluent (in var. confiuens) 

 into a flat, smooth layer 2. R. atra (p 107) 



1. Rivularia Biasolettiana JNIenegh. 



Thallus gelatinous, at first hemispherical, later becoming diffluent 

 and broadly expanded, warty and cushion-shaped, often becoming 

 encrusted with lime, dark olive green, becoming yellowish or brownish 

 on the surface ; filaments densely crowded, 18/a diam. ; sheaths ample, 

 mucous, lamellate, funnelform, hyaline or yellowish, or alternating 

 hyaline and yellowish giving the thallus a zonate appearance ; 

 trichomes 5-9/a diam., prolonged into a delicate, flexuous hair; cells 

 in basal portion slightly shorter than the diameter, one-third the 

 diameter above, heterocyst oblong, basal, 1-3 seriate, or rarel}' inter- 

 calary. 



Growing on dripping rocks in both fresh and salt water along 

 high-tide line and above. Ranging from Unalaska, Alaska, to south- 

 ern California. 



Meneghini, in Zanardini, Syn. Alg. Mar. Adr., 1841, p. 42; Setchell 

 and Gardner, Alg. N.W. Amer., 1903, p. 198 ; Saunders, Alg. Harri- 



