i 
1903] Collins, — The Ulvaceae of North America I5 
Agardh that the Vwa Lactuca of Linnaeus and his immediate suc- 
cessors was a Monostroma, with delicate and much divided frond; 
and that it is the plant distributed as No. 121 of Areschoug, Alg. 
Scand. Exsicc.; it still! remains unlikely that Farlow's M. pulchrum 
is the same plant, as suggested by Agardh. Both Areschoug's plant 
and a specimen of M. Grevi/fei forma Lactuca from Flensburg, deter- 
mined by Hauck, are relatively coarse plants beside M. pulchrum. 
To appreciate the extreme delicacy of typical forms of the latter, one 
must have collected it; it requires as careful handling as the tender- 
est Callithamnion. Reinbold, Chlorophyceen der Kieler Fohrde, 
p. 124, says of M. Lactuca, comparing it with M. Grevi//ei, ** Thallus 
rigider, nicht so schlüpfrig," which is by no means the case with 
M. pulchrum. In structure the European specimens referred to come 
quite near to AM. Greville’, but not to M. pulchrum. While it is 
probable that this species is saccate in its early stages, I know of no 
observation of such a state. Farlow (4) 41. Bennett (1) 95. Col- 
lins (8) 44. Exsicc. Phyc. Bor.-Am., 658. Alg. Am.-Bor., 217. 
5. M. UNDULATUM, Wittr.. Monogr., 47, PI. III, fig. 9, 1866; De 
Toni, Syll. Alg., Vol. L, 105, 1889. Frond membranaceous, soft and 
flaccid, with strongly undulate margin ; 40—50 u thick ; cells angular, 
closely set, showing somewhat of an arrangement in twos, threes, 
and fours; in cross section about 20 high, semicircular or oval; 
the chromatophor not occupying the full height of the cell; not over 
rog in the middle. Plate 41, fig. 12, cross section; fig. 13, surface. 
The typical form, described from Norway, has been found once in 
Greenland by Rosenvinge; the frond is thicker than in any other 
species but M. fuscum, which is not liable to be mistaken for it, 
being amply distinct by its color and consistency. Kjellman (1) 
295. Rosenvinge (1) 945; (2) 149; (3) 117. 
Var. FARLOowr: Foslie, Contrib. I, 114, 1891, excl. syn. Frond 
similar to the type, but less than 30 y thick. 
Foslie and Rosenvinge consider this as identical with M. pulchrum 
Farlow ; but this appears to be a misapprehension, the latter being 
much thinner, with more slender and pointed segments or fronds. 
Greenland, Rosenvinge ; Newfoundland, Holden ; Marblehead, Col- 
lins. Found also in northern Norway. Rosenvinge (1) 945; (2) 
149; both excl. syn. Collins (8) 44. Exstcc. Phyc. Bor.-Am., 406. 
6. M. LEPTODERMUM Kjellm., Algenv. Murmanschen Meeres, 
52, Pl. I, figs. 23-24, 1874 ; De Toni, Syll. Alg., Vol. I, 109, 1889. 
Frond cuneate-obovate, passing by a narrow base into a tubular, 
filiform stipe; the flat part of the frond usually entire, with a more 
or less undulate margin ; often twisted below. Cells in the tubular 
part arranged in longitudinal series, closely set, angular; in flat part 
similar but smaller: membrane 7-10 y thick, cells in cross section 
quadrate or rectangular, 5-8 u high. Plate 41, fig. 10, cross section ; 
fig. 11, surface. 
