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I92.i| Set eh i ll-Giwdm r: Melanophyceae 491
lateral outgrowths from the metamorphosed cells may occur. The
number of erect filaments in proportion to the number of gametangia
is a character which seems to be very unstable. In some collections
they exceed the number of gametangia almost two to one, in others
they do not occur more than in proportion of one to five. They are
very irregular in origin along the radiating creeping filaments. Some
near the margin of the frond may be nearing maturity before others
near the center of the frond have started.
3. Hecatonema clavatum S. and G.
Plate 53, figs. 1-4
Fronds forming circular cushions 2-3 mm. diam., with relatively
wide margin free from erect filaments; prostrate portion attached
by numerous, short, subulate rhizoids, and composed of regularly
radiating, closely crowded filaments; erect filaments mostly clavate,
unbranched, 190-210//. long; cells of creeping filaments 5-6/x diam.,
1.5-2 times as long; cells of erect filaments cylindrical below and
5. 5-6.5//. diam., 2-2.5 times as long, slightly constricted at the dissepi-
ments above and 8-11//. diam., 1.5 times as long; zoosporangia (?)
sessile or subsessile on creeping filaments, clavate, 60-80/a long, 10-1 4/i
broad ; gametangia cylindrical to slightly fusiform, sessile or on short
pedicels on the creeping filaments, 55-85//. (up to 111//.) long, 8-12//.
broad ; locnli mostly 2-seriate.
Growing on the pneumatocysts of Nereoeystis Luetkeana. Mouth
of Tomales Bay, Marin County, California.
Setchell and Gardner, Phyc. Cont. IV, 1922, p. 378, pi. 40, figs. 1-4.
The structures designated zoosporangia (?) in the foregoing diag-
nosis of this species were found interspersed among the gametangia.
No indication of the formation of zoospores has been observed, which
leads to the suspicion that they may be abortive gametangia. The
terminal cell of the erect filaments is often longer than the cells
below it, and in these filaments in which the cells are divided length-
wise, producing the clavate condition, the terminal cell degenerates in
a similar manner as do the hairs in other species. The longitudinal
division of cells in the upper parts of the filaments is undoubtedly
connected w T ith the formation of the short, lateral, often secund, game-
tangia characteristic of nearly related species in Hecatonema and
in Compsonema, for in a few instances such gametangia were observed
in old specimens in wdiich the gametes had, to a large degree, escaped
from the characteristic gametangia.