y smooth and thin, rupturing irregularly;
hypothallus an indistinct membrane or wholly wanting; columella large,
globose or hemispheric, white, the surface granulose; capillitium of
very slender colored threads, the extremities pellucid, more or less
branched; spores violaceous, minutely warted, 9-11 mu.

Growing on old wood, leaves, etc. The sporangium .3-.5 mm., thin and
smooth or rugulose. This elegant little species I know only from
specimens received from Mr. Morgan. It seems to be closely related to
_D. spumarioides_, from which it is distinguished by its color, darker,
and its smoother, or less spinulose spores. The author compares the
color and external appearance to that of _P. cinereum_,--_Jour. Cin.
Soc._, XVI., p. 154.

Ohio, Pennsylvania.

10. DIDERMA HEMISPHERICUM (_Bull._) _Horne._

1791. _Reticularia hemispherica_ Bull., _Cham. de Fr._, I., p. 93.
1829. _Didymium hemisphericum_ (Bull.) Fr., _Syst. Myc._, III.,
p. 115.
1829. _Diderma hemisphericum_ (Bull.) Horne., _Fl. Dan._, XI., p. 18.
1832. _Didymium michelii_ Lib., _Pl. Ard._, No. 180.
1873. _Chondrioderma michelii_ (Lib.) Rost., Fuckel, _Sym. Myc._,
p. 74.

Sporangia gregarious, orbicular, discoid, depressed above and often
umbilicate below, stipitate or sometimes sessile, the outer peridium
white, fragile, crustaceous, soon breaking about the margins, closely
applied to the inner, which is delicate, cinereous, and ruptures
irregularly; stipe about equal to the diameter of the sporangium, 1 mm.,
rather stout, calcareous but colored, brownish or alutaceous, more or
less wrinkled longitudinally, the wrinkles when present forming veins on
the lower surface of the sporangium; hypothallus small; columella not
distinct from the thickened brownish or reddish base of the sporangium;
capillitium of delicate threads, mostly simple and colorless, often
scanty; spores pale violaceous, nearly smooth, 8-9 mu.

A very well marked species, easily recognized, at least when stipitate,
by its remarkable discoid or lenticular sporangia. After the
spore-dispersal, the stipes are long-persistent, surmounted by a
peculiar disk representing the consolidated columella, lower sporangial
wall, and expanded stem-top. Sessile specimens are like similar forms of
_D. reticulatum_, but in all the gatherings before us the stipitate type
is at hand to reveal the identity of the species.

Rostafinski's figures, 131, 146, 149, and 150, adapt