a, Nebraska.

This species presents a decidedly well-marked form, so much so that it
may be easily recognized at sight, without a lens. It therefore requires
special discussion, and although in the spore-characters and some minor
but not determinative details it agrees with _P. virescens_ Ditm. to
which it is by European authors sometimes referred, it seems
nevertheless deserving of specific recognition, since in its entire
habit and expression it is not only completely different but is constant
in its specific peculiarities, much more so than is the suggested
related form.

In the first edition of this work, the form was referred to _Physarum
thejoteum_ of Fries. This was the judgment of our American colleague,
Professor A. P. Morgan whose work in this group is widely recognized.
Fries admits, _Syst. Myc._, III., p. 142, that while he deems _P.
thejoteum_ very distinct, he yet has not seen _P. virescens_ Ditm.!
Since our form apparently does not occur in Europe, specimens which the
distinguished author had before him were doubtless representatives of
the now commonly recognized species of Ditmar.

For these reasons it seems appropriate to give the American type a
suitably descriptive title.

17. PHYSARUM MEGALOSPORUM _Macbr._

PLATE XVI., Figs. 7 and 7 _a_.

1917. _Physarum melanospermum_ Sturgis, _Mycologia_, Vol. IX, p. 323.

Sporangia gregarious, sessile, or short stipitate depressed, annulate,
or at least umbilicate above, white or anon roseate, about .75 mm;
stipe, when present, short, thick, black or dark brown! hypothallus
none; columella none; capillitium strongly calcareous, an abundance of
irregular white nodules burden the delicate net; spores dark sooty brown
with a shade of purple by transmitted light, verruculose, 12-13 mu.

This species is recognizable at once by its regular, uniform, depressed,
annulate or pitted sporangia, scattered evenly over the habitat of
rotten leaves or wood. It suggests a didymium in its form and habit, but
is near a badhamia. Colorado; _Bethel_, 1908.

18. PHYSARUM CONFERTUM _Macbr. nom. nov._

PLATE XV., Figs. 1, 1 _a_, 1 _b_.

1899. _Physarum atrum_ Schw., Macbr., _N. A. S._, p. 36.
1911. _Physarum atrum_ Schw., Lister, _Mycetozoa, 2nd ed._, p. 74.

Sporangia small about .2-.3 mm. in diameter, gregarious, confluent,
clustered or heaped, dull violaceous brown; peridium thin, more or less
transparent, generally limeless but sometimes lightly sprinkled w