172 THE NORTH AMERICAN SLIME-MOULDS 



net parallel to the peridial wall ; peridium evanescent, perhaps some- 

 times not developed at all. 



The genus Comatricha was set off from Stemonitis by the joint 

 effort of Preuss (1851) and Rostafinski (1873-5). Preuss included 

 in his genus, Comatricha, alien forms, and besides failed to give an 

 accurate definition ; included, however, in his list some species which 

 have since been known by his generic name. 



The 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 con- 

 venient. 



Key to the Species of Comatricha 



A. Sporangia closely clustered. 



a. Obovate or short cylindric, 



1. Spores verruculose .... \. 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. 



* Spore-mass brown, spherical, conoidal, etc., generally 

 with more or less lengthened stipe . 8. C. nigra 

 ** Spore-mass violaceous or purplish 9. C. aequalis 

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

 * Cylindric, spore with few, scattered warts 



10. C. typhoides 

 ** Smaller, capillitium irregular, loose 6. C. laxa 

 *** Total height to 2 mm. or much less. 



t Columella digitately divided 



11. C. elegans 



