28o Minnesota Algae 



512. Dichothrix penicillata Zanardini. Plantarum Maris Rubri Enumeratio. 



89. pi. 12. f. 3. 1858. Bornet and Flahault. Revis. des Nostoc. Ann. 

 Sci. Nat. Bot. VII. 3: 379. 1886. De Toni. Syll. Algar. 5: 644. 1907. 



Collins, Holden and Setchell. Phyc. Bor.-Am. Fasc. 2. no. 62. 1895. 

 Collins. The Algae of Jamaica. Proc. Am. Acad. Arts Sci. 37: 242. igoi. 

 Collins, Holden and Setchell. Phyc. Bor.-Am. Fasc. 23. no. 11 12. 1903. 



Plant mass caespitose, fastigiate-penicillate, scattered or gregarious, 

 dark green; filaments 25-35 mic. in diameter, (in ultimate branches), 2 mm. 

 in length, short, flexuous; sheaths thick, gelatinous, soft, uniform, hyaline; 

 trichomes 15 mic. in diameter; cells shorter than the diameter; cell con- 

 tents olive; heterocysts oblong, solitary. 



Mexico. Gulf of Mexico. (Hooper). West Indies. Guadeloupe. 



(Maze). In tufts at joints of Cymopolia barbata. Port Maria, 

 Jamaica. March 1893. (Humphrey). On Dictyota dichotoma. (Pease 

 and Butler). On Digenia simplex. Santurce, Porto Rico. May 1903. 

 (Howe). 



513. Dichothrix utahensis Tilden. American Algae. Cent. III. no. 288. 1898. 

 Setchell. Notes on Cyanophyceae. — III. Erythea. 7: 45. 1899. 



Plant mass impregnated with calcium carbonate, light blue-green, .5-1 

 cm. in thickness; filaments 22-30 mic. in diameter, generally thickened at 

 the base; false branches appressed, included below in the common tegu- 

 ment; sheaths thick, lamellose, colorless or brownish; trichomes 

 7.5-12.5 mic. in diameter, sometimes constricted at joints, tapering into a 

 long hair; cells in lower portions equal to the diameter in length, in upper 

 parts shorter than the diameter; cell contents olive green; heterocysts basal 

 and intercalary, the former one to three in number. 



Utah. Forming a calareous crust on an old board and on stones in a 

 small stream running from a brackish pond into Great Salt Lake, one 

 mile northeast from Black Rock, Garfield Beach. July 1897. (Tilden). 



The above species resembles D. gypsophila and D. calcarea 

 in its habit of forming a calcareous crust and in some minor characters; 

 like Calothrix scopularumit has the basal portion of the filament 

 thickened and often shows two or three basal heterocysts. Dr. Setchel^ 

 refers it to Calothrix parietina, but the filaments are much too 

 large for that species, there are numerous intercalary heterocysts, and it 

 diflfers in several other important characteristics. 



Genus POLYTHRIX Zanardini. Phyc. Indie. Pugillus. 32. 1872. 



Plant mass filiform, branched, consisting of numerous filaments fas- 

 ciculately arranged, included within a common tegument; filaments densely 

 crowded, branched; heterocysts terminal and intercalary. 



514. Polythrix corymbosa (Harvey) Grunow in herb. Bornet and Fla- 



hault. Revis. des Nostoc. Ann. Sci. Nat. Bot. "VII. 3: 380. 1886. Har- 

 vey. Nereis Boreali-Americana. Part. III. 109. pi. 28 B. 1858. (M i- 

 crocoleus corymbosus Harv.). De Toni. Syll. Algar. 5: 645. 

 1907. 



