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REPORT OF THE COMMISSIONER OF FISH AND FISHERIES. 79
A genus of minute algæ which form small brown spots on other plants. The species are ubiquitous, but
the specific characters are not well defined, and a good share of the described species are merely
different forms of the very common M. vulgare. The two different kinds of sporangia are sometimes
found together, but are usually on different plants. The genus is most nearly related to Ralfsia, which
may be said to be a Myrionema in which the horizontal layer has become much thickened, and the
vertical filaments, with the interspersed sporangia, instead of covering the surface uniformly, have
been confined to certain circumscribed portions. The two genera are closely connected by Ralfsia
clavata, Crn., which was first described as a Myrionema by Carmichael. In Ralfsia the vertical
filaments must be considered to be paraphyses, and perhaps those of Myrionema should also be so
considered.
M. VULGARE, Thur. (M. strangulans, Grev.; Phyc. Brit., Pl. 280.—M. punctiforme,
Harv., Phyc. Brit., Pl. 41 b.—M. maculiforme, Kütz., Tab. Phyc., Vol. VII, Pl. 93, Fig.
2.)
Fronds .04-8 mm in thickness, vertical filaments (paraphyses) slightly club-shaped
and moniliform, unilocular sporangia oval, .019-27 mm broad by .03-4 mm long, sessile
or borne on short pedicels.
Everywhere common on various algæ.
In Le Jolis’s Liste des Algues Marines de Cherbourg, Thuret is quoted as authority for uniting several
of the species of Myrionema of Harvey and Kützing. The alleged specific distinctions are plainly nothing
but modifications of the same species, dependent on the place of growth. When found on small
cylindrical fronds, as in some Enteromorphæ, the Myrionema surrounds the frond and constitutes the
M. strangulans of Greville, and when growing on flat surfaces the form known as M. punctiforme is
found. In this country the unilocular sporangia are very common, but we have never seen the
plurilocular sporangia, while in the next species the plurilocular sporangia are more numerous,
although both kinds are found.
M. LECLANCHERII, (Chauv.) Harv., Phyc. Brit., Pl. 41 a. Pl. 6, Fig. 5.
Fronds .06-10 mm in thickness, vertical filaments (paraphyses) cylindrical, unilocular
sporangia oval, plurilocular sporangia .008-10 mm broad by .023-30 mm long, ovate,
oblong, sessile or on very short pedicels.
On Rhodymenia palmata.
Gay Head, Mass.; Europe.
This species forms rather larger spots than the last on the common dulse. That it is really distinct from
M. vulgare admits of doubt. There appears to be a difference in the paraphyses of the two, but such
differences cannot be considered of much value. We have found both unilocular and plurilocular
sporangia in the present species, but unfortunately have not preserved measurements of the latter. The
plurilocular sporangia are sometimes very numerous and stand side by side without intervening
paraphyses.
FAMILY LEATHESIEÆ.
Fronds lubricous or gelatinous, indefinitely expanded or irregularly globose,
consisting of a basal portion, composed of irregularly branching filaments formed of
large, colorless cells, and a cortical portion of closely packed, short, colored
filaments; paraphyses often present;