umber in color, seated on a
broad membranous base, 1.5-2 mm. in diameter; wall wrinkled and usually
marked with small scattered pits, pale-yellow, membranous; walls of
component sporangia, membranous, minutely roughened, perforated with
round openings, the margins of which show many free threads; or reduced
to irregular, anastomosing strands arising from the base of the
aethalium, with membranous or net-like expansions at the angles and with
many delicate, free, pointed ends. Spores pale-yellow, usually united in
twos or threes, and ovoid or flattened on one side; when free, globose,
very minutely spinulose, 9.5-10.5.

Colorado: _Dr. Sturgis._

=3. Dictydiaethalium= _Rostafinski_

1873. _Dictydiaethalium_ Rost., _Versuch_, p. 5.
1875. _Clathroptychium_ Rost., _Mon._, p. 224.

Aethalium depressed, flat; the sporangia erect, regular, prismatic by
mutual pressure, the peridia convex above, wanting at the sides and
within the aethalium represented by vertical threads marking the angles
and passing from base to summit.

This genus is readily recognized by the internal structure of the
aethalium. The lateral wall-openings, which, as we have seen,
characterize the sporangia of the preceding genus, here become extreme,
occupying to such extent the lateral wall-space of each sporangium that
only threads remain to mark the vertical angles.

In 1873 Rostafinski applied the generic name here adopted, because he
thought he discovered close relationships with _Dictydium_. In 1875,
believing his first impressions erroneous, and desirous that the
nomenclature might not at once mislead the student and perpetuate the
memory of his own mistake, the same author proposed the name by which
the genus has generally ever since been known--_Clathroptychium_.
However sensible the latter conclusion reached by our Polish author, it
is plainly contrary to all rules of priority.

Our region shows but a single widely distributed species,--

1. DICTYDIAETHALIUM PLUMBEUM (_Schum._) _Rost._

PLATE I., Figs. 2, 2 _a_, 2 _b_.

1803. _Fuligo plumbea_ Schum., _Enum. Saell._, No. 1410.
1833. _Licea rugulosa_ Wall., _Cr. Fl. Ger._, IV., p. 345.
1873. _Dictydiaethalium plumbeum_ (Schum.) Rost., _Versuch_, p. 5.
1875. _Clathroptychium rugulosum_ (Wallr.) Rost., _Mon._, p. 225.
1894. _Dictydiaethalium plumbeum_ Rost., List., _Mycetozoa_, p. 157.

Aethalium thin, very flat, olivaceous or ochraceous, smooth, under the
lens punctate,