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192.")] SetcheU-Gardner: Melcmophyceae 509
colorless cells with scanty chromatophores, and (:{) a cortical layer
of short, branched, closely compacted, erect filaments composed of
short, colored cells forming; a more or less smooth or wrinkled surface
zoosporangia, embedded within the thallus, more or less cylindrical,
becoming difform, usually attached laterally ;
gametangia unknown.
Xaegeli, in Kuetzing, Tab. Phyc, vol. 8, 1858, p. 2, pi. 3, fig. II.
Comparison of Petrospongium Berkeleyi (Grew) Naeg. with Cylin~
drocarpus microscopicus Crouan reveals such a difference in habit,
structure, etc., that it seems impossible to place the two species in the
same genus. We are also of the opinion that they belong in separate
families. The figures of Cylmdrocarpus microscopicus, especially
those of Kuckuck (1899, p. 88, pi. 6, figs. 1-5) show a plant of definite
habit, growing in tufts (mucose, fide Crouan) rather tending to
elongate although only slightly so. without its individual branched
filaments being agglutinated into the definite thallus with inner
and outer distinct tissues as in the Leathesiaceae, but united into
a spongy (fide Kuckuck) mass by intertwining rhizoidal corticat-
ing filaments. We are inclined to place Cylindrocarpus micro-
scopicus in the Ectocarpaceae, as an extremely differentiated type
of such forms as Eetocarpus liemisphericus and E. chantransioid.es
and looking toward the iEgiraeeae and perhaps, also, the Leathe-
siaceae, but not properly of them or, to the same degree, differen-
tiated into definite inner transparent and outer colored layers.
Petrospongium Berkeleyi (Grev.) Naeg. and P. rugosum (Okamura)
S. and G., especially the latter, have their tissues differentiated and of
agglutinated, level-topped filaments and are, in our opinion, perfectly
typical members of the Leathesiaceae.
Petrospongium rugosum (Okamura) S. and G.
Plate 39, figs. 42, 43
Thallus adhering more or less loosely to the substratum, circular to
irregular in outline, flat or thrown up into folds, more or less spongy
and lubricous, 2.5-5 cm. (up to 10 cm., cf. Okamura) diam., 1.5-2.5
mm. thick, of a dark, glossy, chestnut brown color ; cells of the cortical
layer 8-11//. diam., 1-2 times as long as the diameter ; zoosporangia
narrowly ellipsoidal, at times decidedly difform, attached laterally a
little below the middle and near the base of the cortical filaments,
75-90/x long, 16-22/x broad.
Growing on rocks in the upper littoral belt exposed to surf.
Central and Southern California.
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