calcareous wall conspicuously developed 5. _D. crustaceum_

_b._ Sporangia plainly stipitate.

i. Peridium much depressed; umbilicate below.

O Stipe white 6. _D. squamulosum_

OO Stipe black.

+ Larger, about 7.5-1 mm. 7. _D. melanospermum_

++ Small, about .5 mm. 8. _D. minus_

+++ Sporangia discoid 9. _D. clavus_

ii. Peridium small, globose.

O Stipe dark brown or black; columella
dark, obsolete or none. 10. _D. nigripes_

OO Stipe generally paler, of various tints
of brown, orange, etc.

+ Columella pale or white, nearly
smooth 11. _D. xanthopus_

++ Columella, yellow, discoid, rough 12. _D. eximium_

iii. Peridium turbinate, columella
hemispheric 13. _D. trochus_

iv. Peridium annulate 14. _D. annulatum_

2. Calcareous crystals forming a distinct crust.

A. Fructification wholly plasmodiocarpous 15. _D. dubium_

B. Sporangia ill-defined, sessile, plasmodiocarpous.

_a._ Spores generally nearly smooth 16. _D. difforme_

_b._ Spores very rough, obscurely banded 17. _D. quitense_

EXTRA-LIMITAL

_a._ Sporangia discoid, spores reticulate 18. _D. intermedium_

_b._ Stipe, columella, peridium, orange-brown 19. _D. leoninum_

1. DIDYMIUM COMPLANATUM (_Batsch_) _Rost._

PLATE XVI., Fig. 8.

1786. _Lycoperdon complanatum_ Batsch, _Elench. Fung._, I., p. 251.
1829. _Didymium serpula_ Fr., _Syst. Myc._, III., p. 126, Rost.,
_App._, p. 21.
1875. _Didymium complanatum_ (Batsch), Rost., _Mon._, p. 151.
1899. _Didymium complanatum_ (Batsch) R., Macbr., _N. A. S._, p. 85.
1911. _Didymium complanatum_ Rost., List., _Mycetozoa, 2nd ed._,
p. 127.

Fructification plasmodiocarpous, creeping, flattened, vein-like,
annulate or reticulate, the dark-colored peridium covered with white,
but not numerous crystals; hypothallus none; columella none; capillitium
much branched, violaceous threads combined to form a rather dense net
which bears numerous, peculiar, rounded vesicles, yellowish in color,
30-50