256 THE MYXOMYCETES 



thickened outwardly by a dense reddish or brownish layer of scales, 

 dehiscing by circumscission, cutting off a distinct lid, or, in one 

 species, by areolae ; capillitium often scant, of slender, warted, yellowish 

 threads, sometimes attached to the upper wall; spores yellow, oval or 

 spherical. 



The regular, circumscissile dehiscence is the characteristic mark 

 which distinguishes this genus, as here presented, from Ophiotheca. 

 In general, the tendency toward a plasmodiocarpous development is 

 less marked and the capillitium is less strongly sculptured. Two old- 

 world tropical species, placed here by their authors, are characterized 

 by irregular dehiscence. 



KEY TO THE SPECIES OF PERICILENA 



a. Dehiscence circumscissile b 



a. Dehiscence not circumscissile e 



b. Sporangia greatly flattened; crowded c 



b. Sporangia hemispherical or subglobose; less crowded or 



gregarious d 



c. Individual sporangia 0.5-1 mm. or more in diameter I. P. depressa 



c. Individual sporangia 0.1-0.4 mm. in diameter 2. P. quadrata 



d. Chestnut brown; spores 10-12 /z 3. P. corticalis 



d. Gray or canescent; spores 12-15 /u 4. P. marginata 



e. Dehiscence areolate; purplish black 5. P. tessellata 



e. Dehiscence irregular / 



/. Plasmodiocarpous; salmon pink 6. P. microspore! 



f. Sporangiate, stalked; purplish 7. P. pulcherrima 



1. Pericilena depressa Libert 



Fl. Crypt. Ard. fasc. 4, No. 378. 1837. 

 PI. XVII, Figs. 433, 434. 



1842. Stegasma depressum (Lib.) Corda, Icones 5 : 58. 



1873. Perichcena artocreas Berk. & Rav., Grev. 2 : 68. 



1873. Perichcena irregularis Berk. & Curt., Grev. 2 : 68. 



1874. Stegasma australe Ces., Hedwigia 13 : 186. 



1876. Perichcena marginata Berk. & Br., Jour. Linn. Soc. 15 : 84, non Schw. 



1887. Hemiarcyria applanata Cooke & Mass., Grev. 16 : 20. 



1888. Perichcena australis (Ces.) Berl., in Sacc, Syll. 7 : 422. 

 1892. Perichcena applanata (Cooke & Mass.) Massee, Mon. 116. 

 1892. Ophiotheca irregularis (Berk. & Curt.) Massee, Mon. 132. 



Sporangia sessile, applanate, crowded, polygonal by mutual contact, 

 fuscous to chestnut brown, shining, opening by a definite lid; spore- 

 mass and capillitium yellow, the capillitium well developed, almost 

 smooth, of slender yellow threads of various widths; spores minutely 

 warted, 10-12 fx. 



