472 University of California Publications in Botany [^'^ol. 6 



or less branched and which is commonly less firm and in some cases 

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

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

 end cell walls. Borzi, however, has placed a species from New Guinea 

 in this genus although it is but 2/a in diameter. 



Microcoleus confluens does not conform wholly to the characters of 

 either of the two above mentioned genera. It has the few trichomes 

 and diffluent sheath of a typical Hydrocoleum but has the small tri- 

 chomes of a typical Microcoleus. 



Calothrix rectangularis Setchell et Gardner sp. nov. 



Plate 40, fig. 21 



Fills simplicibus aut interdum parce pseudoramosis, basim algis 

 variis affixis, juvenis prostratis, mox erectis, 400-500/i, altis, ad basim 

 24-28ja diam. ; trichomatibus basim 16-18ja diam., superne usque ad 

 sub apicem longe attenuatis delude in pilo brevi abeuntibus : cellalis 

 2-4^ longis, cytioplasmate tenui granulato, dilute coeruleo-viridi ; 

 vaginis juvenis hyalinis, aetate provecta dilute luteis, ad apices 

 strictis; heterocystis basilaribus et intercalaribus, basilaribus sphaer- 

 icis aut subconicis, intercalaribus plus minusve elongato-cylindricis 

 pro parte majori singulis et prope basim triehomatis, 18-25/^ longis 

 et 16-18/x diam. 



Filaments simple or occasionally sparsely branched, attached at 

 the base to various other algae, prostrate when young, soon becoming 

 erect, 400-500/x long, 24-28/* diam. at the base; trichomes 16-18/x 

 diam. at the base, tapering gradually upward nearly to the apex, then 

 rather abruptly ending in a short hair; cells 2-4/i, long, protoplasm 

 finely granular, pale blue-green ; sheath hyaline when young, chang- 

 ing to light yellow with age, strict at the apex ; heterocysts basal and 

 intercalary, the basal spherical to subconical, the intercalary cylind- 

 rical, usually single, near the base of the trichome, 18-25,a long, tlie 

 same diameter as the trichome. 



Epiphytic on various species of marine algae, near low-tide level. 

 East Sound, Orcas Island, Washington. Type no. 2365, Gardner. 



This species comes within the range of measurements stated hy 

 Bornet and Flahault (Rev. I, 1886, p. 359) for the diameter of the 

 filaments of C. Crustacea Thuret with which it seems to be most closely 

 related ; the filaments are, however, much shorter than the measure- 

 ments given for that species. The small size, the habit of growth on 

 other algae, the presence of cylindrical, intercalary heterocysts 

 always near the base of the trichomes, the infrequency of branching, 

 and the strict sheath seem sufficient to separate this species from any 

 of the forms of C. Crustacea. The cylindrical heterocysts above men- 

 tioned, appearing rectangular to the view, are sufficiently striking to 

 suggest the specific name. 



