distinction between the two genera is almost an artificial one, and
species are sometimes arbitrarily assigned to one genus or the other.
The diagnosis in any case turns upon the presence or absence of a
surface net, formed, in _Stemonitis_, by the anastomosing of the
ultimate divisions of the capillitial branches. In _Comatricha_ the
anastomosing is general, from the columella out, and is not specialized
at the surface.

Recent attempts to reunite the genera here compared seem to result in no
apparent advantage. The genera come very near together, but their
separation along the line suggested by Rostafinski remains convenient.

=Key to the Species of Comatricha=

_A._ Sporangia closely clustered.

_a._ Obovate or short cylindric.

1. Spores verruculose 1. _C. caespitosa_

2. Spores reticulate 2. _C. cylindrica_

_b._ Elongate, reddish-brown, tufts extended 3. _C. flaccida_

_B._ Sporangia scattered more or less widely.

_a._ Capillitium lax, open.

i. Sporangia long, 10-12 mm. 4. _C. longa_

ii. Sporangia shorter, capillitium
irregular 5. _C. irregularis_

_b._ Capillitium dense.

i. Sporangia large, to 10 mm., spore-mass
black 7. _C. suksdorfii_

ii. Sporangia smaller--6 mm.

O Spore-mass brown, spherical,
conoidal, etc., generally with
more or less lengthened stipe 8. _C. nigra_

OO Spore-mass violaceous or purplish 9. _C. aequalis_

iii. Sporangia ovate or cylindric, minute,
to 3.5 mm.

O Cylindric, spore with few,
scattered warts 10. _C. typhoides_

OO Smaller, capillitium irregular,
loose 6. _C. laxa_

OOO Total height to 2 mm. or much less.

+ Columella digitately divided 11. _C. elegans_

++ Columella lamprodermoid, and on
leaves 12. _C. rubens_

+++ Columella stemonitoid 13. _C. pulchella_

++++ Columella furcate at tip 14. _C. ellisii_

+++++ Columella al