i. Sporangia as if interwoven,

compressed 9. _P. contextum_

ii. Sporangia more nearly free, distinct.

o Spores pale, inner peridium brittle 10. _P. conglomeratum_

oo Spores spinulose, dark violet 11. _P. mortoni_

_c._ Sporangia brown, dehiscence revolute 12. _P. brunneolum_

2. Peridium simple, calcareous, flaky.

_a._ Sporangia grey, plasmodiocarpous; spores dusky, 10-12 forms of 3

_b._ Sporangia grey, more or less dense; spores violet, 6-7 13. _P. cinereum_

_c._ Calcareous deposits yellow or greenish, spores 7-9 14. _P. virescens_

_d._ Sporangia rusty or reddish brown, more or less dense 15. _P. rubiginosum_

_e._ Sporangia minute, lignicolous, the fructification much extended upon a hypothallus, lime deposit tawny 16. _P. instratum_

_f._ Sporangia white, depressed, annulate, sometimes with short stipes 17. _P. megalosporum_

3. Peridium simple, not flaky, small .2-.3 mm., heaped 18. _P. confertum_

B. Sporangia, at least some of them, stipitate.

_a._ Sporangia columellate.

i. Columella small, usually conical.

O Sporangium yellow.

o Columella white 19. _P. melleum_

oo Columella yellow 20. _P. citrinum_

OO Sporangium not yellow.

o Capillitial mass persistent.

+ Sporangia globose, pallid or white 21. _P. globuliferum_

++ Sporangia blue or lilac, rose, etc. 22. _P. lilacinum_

+++ Sporangia drab or brownish 23. _P. murinum_

++++ Sporangia wine-red 24. _P. pulcherrimum_

oo Capillitial-mass less persistent; orange 25. _P. pulcherripes_