364 TUFTS COLLEGE STUDIES, VOL. II, No. 3 



3. P. CLEVEANA Wittrock, 1877, p. 58, PL II, figs. 13-15 ; 

 PL IV, figs. 12-18; PL V, figs. 1-8. Main filaments about 75/0. 

 diam., branches usually of the first order only, occasionally 

 with a few short, scattered or opposite branches of the second 

 order ; special helicoid cells frequent ; akinetes intercalary or 

 terminal, solitary, rarely in twos ; intercalary akinetes cask- 

 shaped, 2oo-26oX 100-160 /j., or subcylindrical, about 165X70 ^ ; 

 terminal akinetes cask-shaped with shortly acuminate rounded 

 apex, 175-240X90-105 /j.. Fla., St. Thomas, Barbados. 



4. P. VARIA Wille, P. B.-A., No. 983 ; P. Kewensis Tilden, 

 Amer. Algae, No. 39. Filaments 75-105 /j., primary and sec- 

 ondary branches about the same ; terminal cells 43-70 /*, rarel} r 

 ending in helicoids ; akinetes i-3-seriate, with wall, especially 

 end wall, quite thick, terminal and intercalary, arising in main 

 stem or in branches of any order ; terminal akinetes ovoid, with 

 pointed tip, 150-210X64-69 n- ; intercalary 70-240X60-112 /x ; 

 ovoid, cylindrical or irregular. 111., Mich., Minn. 



The only species of Pithophora native in colder regions. 

 Nearest related to P. Cleveana Wittr. , but differing in several 

 characters. The akinetes occur even in the shortest branches, 

 some branches consisting of two akinetes and nothing else. 

 The form of the akinetes differs much in the same branch, and 

 series of 2 or 3 are found including every possible combination 

 of cylindrical, ovoid and irregular forms. P. Kewensis Tilden, 

 No. 39, is identical with P. varia ; P. Kewensis Wolle, 1887, p. 

 131, is founded on sterile plants, and cannot be considered 

 reliable. 



5. P. ROETTLERI (Roth) Wittrock, 1877, p. 66, PL I, figs. 

 12-20; PL V, figs, ii and 12 ; Cladophora Engelmanni Kiitzing, 

 1849, p. 411. Main filaments about 165 p. diam., branching of 

 three orders ; branches of the first order in whorls of three or 

 more ; of second and third orders scattered or opposite ; akin- 

 etes solitary, rarely in twos, intercalary or terminal ; in the 

 main filaments of irregular and var}dng shape, about 210X190 

 /A; in the branches cask-shaped, about 260X150^, or cylindri- 

 cal, about 140X80 p.; terminal akinetes obovoid with truncate 

 base, about 210X150 /x, or more rarely subconical with rounded 

 apex, about 250X90^. Cuba, Ark., in warm springs. 



Asia, So t . America. 



Hawaiian specimens, and differs from P. oedogonia by less compound 

 branching, no branches from cells below akiuetes, and akinetes varying 

 much in size, but proportionally stouter than in P. oedogonia. 



