238 TJniversity of California PuNications in Botany [Vol. 8 



2. Monostroma arcticum Wittr. 



Frond attached, at first saccate, later splitting into a few broad 

 laciniae ; subradiately plicate, with crisped margin ; pale green, becom- 

 ing yellowish in drying; membrane 25-45/a thick; cells 4-6 angled, 

 closely set, irregularly placed ; in cross section either vertically or 

 horizontally oval, 10-30/a high. 



On stones, in shallow pools of the middle littoral belt. Known 

 only from Alaska. 



Wittrock, Monostr., 1866, p. 44, pi. 2, f . 8 ; Collins, Green Alg. 

 N. A., 1909, p. 210; Setchell and Gardner, Alg. N.W. Amer., 1903, 

 p. 208; Collins, Holden and Setchell, Phyc. Bor.-Amer., (Exsicc), 

 no. 910. Monostroma latissimiom Setchell and Gardner, Alg. N.W. 

 Amer., 1903, p. 207 (in part). 



Rosen vinge (1893, p. 949, 1894, p. 152) unites Monostroma 

 arcticum with M. Grevillei, keeping it as a variety. Much may be 

 said in favor of such a disposition, especially in view of the treatment 

 usually accorded 31. fuscum, M. spleiidens and M. BUjttii. Collins 

 (1909, p. 210), however, decides to keep them separate, although 

 acknowledging the close relationship, on the ground that M. arcticum 

 is a somewhat tougher and thicker plant than typical M. Grevillei. 

 It seems best to us, also, to keep them separate. We follow Rosen- 

 vinge, however, in uniting with Monostroma arcticnm, M. angicava, 

 M. cylindraceum and M. saccodeum of Kjellman (1883, pp. 295-297). 

 These last species seem to differ only in general habit and this is prob- 

 ably due to earlier or later splitting of the saccate frond. 



We find in carefully examining some specimens from Bering Sea 

 and northwestern Alaska, previously referred (cf. Setchell and Gard- 

 ner, 1903, p. 207, as to nos. 4020 and 5077) to Monostroma latissium, 

 that they agree better with M. arcticum. 



3. Monostroma zostericola Tilden 



Plate 14, figs. 12, 13 



Frond more or less cucullate, cuneate-obovate or divided into 

 segments of that form; cells angular, in more or less distinct series, 

 longitudinal and transverse ; margins plane, often ragged ; membrane 

 7-10/A thick, cells quadrate to vertically oblong in cross section, 5-8/a 

 high. 



