xxxx. 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, clustered, 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_