16 Rhodora [JANUARY 
This species has the most delicate frond of all in the genus, except 
M. pulchrum. It is found; in Greenland in many places, growing 
below low water mark or in pools. It occurs also in Nova Zembla. 
In young plants the filiform stipe is short and inconspicuous ; it 
appears to continue growing during the life of the plant, reaching a 
length of two or three cm. Plants collected by the writer at Nahant 
in June, 1882, and at Cohasset, Mass., in April, 1883, have the mem- 
branous part of the frond the same as in Greenland specimens; the 
stipe, however, is quite inconspicuous, ‘They would seem to belong 
to this species, possibly imperfectly developed from being so far 
south of its ordinary range. Apart from the stipe, the chief char- 
acters are the thinness of the frond, approached only by M. pulchrum ; 
and the squarish cells, regularly arranged, almost like a Prasiola. 
M. zostericolum ‘Tilden, American Algae, No. 388, seems to be iden- 
tical with the plant from Cohasset. As Rosenvinge notes that young 
plants with very short stipe grew in company with older, long-stiped 
individuals, it would seem better to include all the forms in question 
under M. Jeptodermum, without distinction, even as form. Rosenvinge 
(1) 944, fig. 49 ; (2) 149, fig. 49; (3) 117. Collins (8) 44. 
7. M. cREPIDINUM Farlow (1) t4, 1881; J. G. Agardh, Till Alg. 
Syst, part 3, ror, 1882; De Toni, Syll. Alg., Vol. L, 103, 1889. 
Frond delicate, light green, 5-15 cm. long, flabellately orbiculate, 
when fully developed split nearly or quite to the base, segments obo- 
vate; membrane 18-36, rarely 45 » thick; cells roundish-angular, 
when actively dividing forming compact groups of 2, 3, or 4, separated 
by rather wide spaces. Plate 41, fig. 14, cross section; fig. 15, surface. 
One of the smaller species of the genus, confined to the Atlantic 
Coast of the United States, on which it is rather common from Cape 
Cod to New Jersey, and found also at Salem harbor, Mass. A favor- 
ite habitat seems to be on woodwork between tide marks, but it also 
grows on rocks ; it is usually in rather dense tufts, which have a rich 
dark green color, though the individual frond is light green. It is 
found in spring and summer. The form varies from a flat, roundish, 
undivided frond, slightly lobed at the margin, to a frond cut nearly 
to the base into several segments, and radially much plicate. Under 
the microscope, there usually appear several quite distinct starch 
granules in each cell. Farlow (4) 42. Collins (1) 70; (3) 310; 
(6) 77: (8) 44. Martindale (1) 92. Britton (1) 4oo. Exsicc. 
Phyc. Bor.-Am., 229. Alg. Am.-Bor., 174. 
8. M. LATISSIMUM (Kütz.) Wittr., Monogr., 33. Pl. I, fig. 4, 1866. 
J. G. Agardh., Till Alg. Syst., part 3, 99, 1882; De Toni, Syll. 
Alg., Vol. I, 102, 1889. 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 y thick, cells 4-6 
cornered or roundish, closely set, without order or more or less dis- 
tinctly in twos, threes or fours; in cross section vertically oval or 
