s, and whose spores are 8 mu. But even here the
chances of error are small. In the species last named the columella or
sporangial base is alutaceous, not white; in Fries' species, while the
columella if present may be white, the peridial walls are different,
difficult to distinguish.

For these reasons, _D. globosum_ Pers. may stand, waiting further light
from Europe.

5. DIDERMA CRUSTACEUM _Peck._

PLATE VII., Fig. 7

1871. _Diderma crustaceum_ Peck, _Rep. N. Y. Mus._, XXVI., p. 74.
1889. _Chondrioderma crustaceum_ (Peck) Berl., _Sacc._, VII., p. 373.

Plasmodium at first watery, colorless, becoming at length milky white;
sporangia closely crowded or superimposed, in a cushion-like colony,
creamy white, globose, imbedded in the substance of the hypothallus, the
outer peridium smooth, delicate, crustaceous, fragile, remote from the
blue iridescent inner membrane; hypothallus prominent; columella
variable, generally present, globose; capillitium dark-colored, the
threads branching and combining to form a loose net; spore-mass black,
spores by transmitted light dark violaceous, delicately roughened, 12-15
mu.

Common. Readily to be distinguished from the preceding by the larger
spores and more crowded habit. New England west to Nebraska.

The didermas are generally delicately beautiful. The outer wall in the
present species is like finest unglazed china, softly smooth, and yet
not polished, often absolutely white, with porcellanous fracture. An
inter-parietal space separates the outer from the inner wall, so that
the former may be broken, bit by bit, without in the least disturbing
the underlying structure. The inner wall is ashen or gauzy iridescent
green, sending back all colors in reflected light. The spores are
violet, deeply so when fresh, the capillitium strong and likewise
tinted; the columella passing down and blending with the common
snow-white hypothalline base. The distinct habits of the two species are
represented in Figs. 5 and 7. In the one the distinct sporangia are
associated but not crowded; in the other all are massed together in
quite aethalioid fashion, forming circumambient, chalky masses of
considerable size, 2 or 3 cm., overcrowded, superimposed, where the
sporangia are regular in shape and size by reason of mutual pressure.
The plasmodium develops in forests and orchards, among decaying leaves,
but is inclined to rise as maturity draws near, to ascend some twig
erect, or the stem o