88 University of California Publications in Botany [Vol. 8 



.V. \V((ksii is a species which seems at present to have its nearest 

 affinities witli .1/. chthonoplastes (Mert.) Thnret, on the one liaiid, 

 and .1/. aciitirostris (Crouan) Gomont, on the other. It differs from 

 the first in the character of the sheath, being very much more indefi- 

 nite, gelatinous, and amorphous, in liaving fewer trichomes within the 

 sheath, and in the trichomes being larger as well as the cells much 

 shorter. From tlie latter species it differs in having smaller trichomes 

 witli shorter cells, in not having the ends long, attenuated and verj^ 

 acute-conical as has M. aciitirostris, according to the figures and 

 description given bj'' Crouan. The trichomes in M. Weeksii begin to 

 taper about 6-10 cells back of tlie apices. 



4. Microcoleus confluens S. and G. 

 Plate 6, fig. 25 



Filaments erect, forming a blue-green, compact, spongy stratum 

 of indefinite expansion on rocks ; sheath gelatinous, moderately ample, 

 irregular on the surface, hyaline, homogeneous, distinct at first or 

 later diffluent ; trichomes 1-8 in a sheath, separate or lossely entwined, 

 very slightly constricted at the dissepiments, 4-4.5ju, diam., straight 

 and not attenuated at the apices ; cells 2-4 times shorter than the 

 diameter, protoplast homogeneous; apical cell moderately rounded, 

 end wall slightly thickened. 



Forming a spongy- stratum in company with other species of 

 Myxophyceae on rocks in the upper part of the littoral belt. Lands 

 End, San Francisco, California. 



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

 p. 471, pi. 40, fig. 25. 



The species of the genera 3Iicrocoleus and Hydrocoleum inter- 

 grade, at least to a certain extent. Tj^pical Microcoleiis includes forms 

 with numerous entwined trichomes within firm, fairly regular, un- 

 branched sheaths. The trichomes are usually small, more or less 

 pointed at the ends, mostly ranging below 7/x in diameter, except 

 M. suhtorulosus which is 6-10/i, in diameter, and the cells are gen- 

 erally longer than the diameter. 



The majority of the species which have thus far been placed in 

 Hydrocoleum have fewer trichomes in a sheath, which is often more 

 or less branched, and which is commonl}^ less firm and in some cases 

 even wholly diffluent. The trichomes are large, as a rule, with cells 

 shorter than the diameter, the end cells usually blunt with thickened 



