1U4 University of California Fuhlications in Botany [Vol.8 



2. Dichothrix minima S. and G. 



Filaments forming small, dense clusters 80-140/a high ; trichomes 

 few, 2-5, and almost wholly included within the common sheath, pale 

 aeruginous, tapering gradually upward from the heterocj-st, slightly 

 torulose, ending in a long hyaline hair; basal cells 4r-oix diam., quad- 

 rate or slightly longer, homogeneous ; hair cells 0.8-1/a diam. ; lietero- 

 cysts basal, single, spherical or subconical, slightly' larger than the 

 trichomes ; sheath strict, at first hj'aline, soon becoming brown and 

 distinct. 



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

 p. 474. 



Growing in small tufts on Enteromorpha sp. along high-tide level 

 and above. Chuekanut Quarry near Bellingham, Washington. 



The type material of Dichothrix minima was collected in July, 

 1899. There was a very small quantity and it was placed in the 

 Herbarium of the University of California under no. 100,341, awaiting 

 the accumulation of other material. The locality has not been revisited 

 and other material has not been reported from elsewhere. It is hoped 

 that this description may stimulate further search for it. 



27. Isactis Thuret 



Filaments erect, parallel, densely crowded, and coalescent into a 

 compact layer attached to the substratum, simple or sparsely branched ; 

 heterocysts basal ; reproduction by spores unknown. 



Thuret, Essai Class. Nost., 1875, pp. 376, 382; Bornet and Fla- 

 hault, Rev. I, 1886, p. 343. 



The diagonsis given by Thuret {loc. cit., p. 376) was short, but yet 

 to the point. Isactis is a habit genus differing from Rivularia in its 

 more simple trichomes which are crowded and parallel. This gives 

 rise to flattened, more or less orbicular layers instead of spherical, 

 hemispherical, or more or less convex and lobed expansions. 



Isactis plana (Harv.) Thuret 



Fronds scarcely 0.5 mm. thick, spread out indefinitely on the 

 surface of rock, dark green ; filaments densely crowded, mostly simple ; 

 trichomes 7-9/i, diam., light blue-green, tapering into a delicate hair 

 above when young. 



