rystalline character of
its crust. This is a very marked structure; loosely built up of very
large crystals, it is necessarily extremely frail, nevertheless
persists, arching over at a considerable distance above the peridium
proper. Sometimes, however, caducous, evanescent.

The sporangia are said to be sometimes stipitate. This feature does not
appear in any of the material before us. Lister in _Mycetozoa_ Pl. XL.,
_c._ draws the capillitium much more delicate than it appears in our
specimens. The hypothallus is sometimes noticeable under some of the
sporangia where closely crowded, but is not a constant feature.

Rostafinski (by typographical error?) confused in the _Monograph_, pp.
164, 165, this species with Persoon's _Physarum confluens_. In the
_Appendix_ he substitutes the Friesian nomenclature. Persoon's
description of his species is insufficient, and throws no light on the
problem whatever.

Rare. Iowa; Black Hills, South Dakota. Reported common in Europe.
Canada; Vancouver Island to the St. Lawrence.

6. DIDYMIUM SQUAMULOSUM (_Alb. & Schw._) _Fries._

1805. _Diderma squamulosum_ Alb. & Schw., _Consp. Fung._, p. 88.
1816. _Didymium effusum_ Link, _Diss._, II., p. 42.
1829. _Didymium squamulosum_ (Alb. & Schw.), Fries, _Syst. Myc._,
III., p. 118.
1875. _Didymium effusum_ (Link) Rost., _Mon._, p. 163.
1894. _Didymium effusum_ (Link) List., _Mycetozoa_, p. 99.

Sporangia, in typical forms, gregarious, globose or depressed-globose,
gray or snow-white, stipitate; the peridium a thin iridescent membrane
covered more or less richly with minute crystals of lime; the stipe when
present, snow-white, fluted or channelled, stout, even; columella white,
conspicuous; hypothallus usually small or obsolete; capillitium of
delicate branching threads, usually colorless or pallid, sometimes with
conspicuous calyciform thickenings; spores violaceous, minutely warted
or spinulose, 8-10 mu.

This, one of the most beautiful species in the whole series, is
remarkable for the variations which it presents in the fruiting phase.
These range all the way from the simplest and plainest kind of a
plasmodiocarp with only the most delicate frosting of calcareous
crystals up through more or less confluent sessile sporangia to
well-defined elegantly stipitate, globose fruits, where the lime is
sometimes so abundant as to form deciduous flaky scales. The
hypothallus, sometimes entirely wanting, is anon well devel