_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 ma.s.s 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-ma.s.s less persistent; orange 25. _P. pulcherripes_

ii. Columella long, 4-5 the sporangium non-calcareous. 26. _P. penetrale_

iii. Columella large globose 27. _P. luteo-alb.u.m_

_b._ Sporangia without columella.

i. Sporangia nucleate, calcareous at center.

O Stipe yellow 28. _P. nucleatum_

OO Stipe white 29. _P. wingatense_

ii. Sporangia non-nucleate.

O Sporangia purple 30. _P. newtoni_

OO Sporangia blue, spotted with red 31. _P. psittacinum_

OOO Grey or white, iridescent betimes.

o Sporangia white, discoidal; stipe yellow 32. _P. discoidale_

oo Sporangia lightly calcareous, iridescent, sub-globose, diam. about = to the stout, brown, slightly wrinkled stipe 33. _P. leucophaeum_

ooo Sporangia globose or sub-globose.

x. Small, .5 mm.

+ Stipe erect, clear brown 34. _P. nodulosum_

++ Stipe weak, yellow, stuffed 35. _P. maculatum_

xx. Larger, lime-capped; stipe strand-like 36. _P. didermoides_

x.x.x. Stipe snow-white, fragile 37. _P. leucopus_

x.x.xx. Stipe generally distinctly fluted

+ Sporangia laterally compressed, fan-shaped 38. _P. compressum_

++ Sporangia typically globose, umbilicate below, connate, etc., strongly calcareous 39. _P. notabile_

+++ Sporangia reniform, concave below _P. affine_, see under 38

++++ Sporangia larger, to 1 mm., nearly limeless, iridescent 40. _P. tropicale_

oooo Sporangia obovate, compound, cl.u.s.tered, the stipe fuscous, fluted, short. 41. _P. nicaraguense_

OOOO Sporangia yellow, rarely iridescent or brown.

o Capillitial nodes white.

x. Stipe also white 42. _P. sulphureum_

xx. Stipe flesh-colored, spores smaller 43. _P. carneum_

x.x.x. Stipe red or reddish brown 44. _P. citrinellum_

x.x.xx. Stipe yellowish, flaccid, sporangia leocarpine 45. _P. albescens_

x.x.xxx. Stipe very short or none, sporangia cylindric, brown 46. _P. variabile_

oo Capillitium nodes yellow or orange-yellow.

x. Badhamioid, larger,--to .8 mm. 47. _P. auriscalpium_

xx. Physaroid, base persistent 48. _P. oblatum_