12 Rhodora [JANUARY 
isade form” in cross section; and M. splendens with deep green 
glossy frond, 50-55 m thick, more deeply parted than the others, with 
cells similar to M. BZyttii or more rounded. ‘These three forms pass 
into each other with no dividing line, while they are sharply marked 
off from all other species of the genus in nearly every respect. The 
very young plant is in the form of a closed tube, which soon splits 
down one side, and spreads out to form a flat membrane; not split- 
ting into several segments, as in the M. Grevi//ei group. 
Forma BLvrTU (M. B/yttiz, Wittr., Monogr., 49, Pl. III, fig. 11, 
1866) is common from Nahant northward and has been found at New- 
port, R. L, by Mrs. Simmons; it grows in tide pools, and also on 
pebbles in the sublitoral zone; at Revere Beach, Mass., great 
quantities are sometimes washed ashore by November storms, the 
stones on which they grew remaining attached to them. In Green- 
land it is reported as found from Jan. to March, and from May to 
Sept.; very young plants being found in June. On the Massachusetts 
coast it makes its appearance in Sept., and reaches its full develop- 
ment in Nov. and Dec. The thinner form which apparently should 
be considered the typical M. fuscum appears to be less common, but 
is found at Greenland and in Alaska. Plate 41, fig. 2, cross section ; 
fig. 3, surface. 
Forma SPLENDENS (M. splendens Wittr., Monogr., 50, Pl. III, fig. 
12, 1866) occurs in the northern Pacific, in Bering Sea and vicinity, 
passing into forma /y/tiz, which occurs nearly typical at Victoria, 
B. C., and in Washington. i 
In one form or another the species probably occurs throughout the 
Arctic Ocean. Kjellman (1) 299; (2) 54. Rosenvinge (1) 940, 
figs. 47-48 ; (2) 145, figs. 47—48 ; (3) 116. Collins (8) 44. Saunders 
(1) 409. M. Blyttii Farlow (4) 41; (5)477. Collins (1) 7o. Britton 
(1) 400. M. splendens Kjellman (2) 54. Setchell (1) 591. Exsicc. 
Phyc. bor.-Am., 715, 911; Alg. Am.-Bor., 98. 
2. M. GnEviLLEI (Thuret) Wittr., Monogr., 57, Pl. IV, fig. 14, 
1866; J. G. Agardh, Till Alg. Syst., part 3, ror, 1882; De Toni, Syll. 
Alg., Vol. I, 103, 1889. Frond attached, at first saccate, then open- 
ing at the top, and ultimately splitting to the base; soft and delicate, 
pale green; membrane 15-20 p thick, cells quadrate with rounded 
angles, closely set; in cross section horizontally oval, 12-14 y high. 
Plate 41, fig. 4, cross section; fig. 5, surface. 
The saccate form is plain in young plants, and may persist for 
some time when growing in still water; but at exposed points the 
frond is soon torn open, and in mature plants all trace of the original 
shape is lost, wherever growing. According to Rosenvinge, Gren- 
lands Havalger, p. 948, the specimens from Greenland referred to 
M. lubricum Kjellman, in Algae Arctic Sea, p. 295, are M. Greviliei. 
M. crassiusculum Kjellman, Om Beringhafvets Algflora, p. 53, Pl. 
VII, figs. 13-15, seems from the description and figures to be hardly 
