THE GREEN ALGAE OF NORTH AMERICA 211 



5. M. PULCHRUM Farlovv, 1881, p. 41 ; P. B.-A., No. 658. 

 Frond divided into linear or lanceolate segments with slender 

 base, much crisped at the margin, light green, membrane about 

 6 p. thick in the upper part, up to 15 p. near the base, cells 

 roundish, rather irregular in form. 



A beautiful species, extremely delicate, adhering so closely to 

 paper when mounted that it is almost impossible to detach it for 

 examination. It occurs on rocky shores, usually epiphytic on 

 other algae, from April to June. Newfoundland to R. I. 



6. M. UNDULATUM Wittrock, 1866, p. 46, PI. Ill, fig. 9. 

 Frond membranaceous, soft and flaccid, with strongly undulate 

 margin ; 40-50 p. thick ; cells angular, closely set, showing 

 somewhat of an arrangement in twos, .threes, and fours; in 

 cross section about 20 //. high, semicircular or oval ; chromato- 

 phore not occupying the full height of the cell ; not over 10 //. in 

 the middle. Greenland. Northern Europe. 



The typical form has a thicker frond than any other species 

 but M. fuscum, which is not likely to be mistaken for it, being 

 amply distinct by its color and consistency. 



Var. FARLOWII Foslie, 1890, p. 114; P. B.-A., No. 406. 

 Frond similar to the type, but less than 30 p. thick. Greenland 

 to Mass. Norway. 



7. M. CREPIDINUM Farlow, 1881, p. 42; P. B.-A., No. 220. 

 Frond delicate, light green, 5-15 cm. long, flabellately orbicu- 

 late, when fully developed split nearly or quite to the base, seg- 

 ments obovate ; membrane 18-36, rarely 45 /".thick ; cells round- 

 ish-angular, when actively dividing forming compact groups of 

 2, 3, or 4, separated by rather wide spaces. Mass, to N. J. 



On woodwork between tide marks, also on rocks ; it is usually 

 in rather dense, tufts, which have a rich dark green color, 

 though the individual frond is light green. It resembles in 

 habit the European M. Wittrockii, but has a thicker frond, with 

 cells more elongate horizontally in cross section. M. Wittrockii 

 is more membranaceous in texture, not adhering well to paper. 



8. M. LATISSIMUM (Kiitz.) Wittrock, 1866, p. 33, PI. I, fig. 

 4; P. B.-A., Nos. 14, 1122. Frond at first attached, afterwards 

 floating ; thin and soft, glossy, of irregular shape, more or less 

 plicate near the even or undulate margin ; membrane 20-25 P- 

 thick, cells 4-6-cornered or roundish, closely set, without order 

 or more or less distinctly in twos, threes, and fours ; in cross 

 section vertically oval or nearly circular, 14-18 n high. Me. to 

 Fla.; Alaska to Washington. Europe, Africa, New Zealand. 



