126 THE MYXOMYCETES 



Sporangia sessile, white, crowded, spherical or by mutual pressure 

 irregular; peridium plainly double, but the layers adhering, the outer 

 more strongly calcareous, but very frail, almost farinaceous; hypo- 

 thallus more or less plainly in evidence, white or pale alutaceous; 

 columella distinct, though often small, globose, white or yellowish; 

 capillitium variable in quantity, sometimes abundant, brown, some- 

 what branching and anastomosing outwardly, the tips paler; spores 

 distinctly but rather sparsely warted, dark violaceous, 8-11 ix. 



This species has the outward seeming of a didymium, but is plainly 

 different as that genus is here defined, since the calcareous crust, al- 

 though inclined to be pulverulent, is made up of minute granules, not 

 crystals, of lime. The hypothallus is sometimes hardly discoverable, 

 sometimes well developed, rugulose, extending far beyond the limits of 

 the fructification. In the Monograph, p. 175, Rostafmski includes here 

 Physarum stromateum Link. In the Appendix he is inclined to raise 

 Link's form to the dignity of a distinct species, basing the diagnosis 

 upon the superposition of the sporangia in certain cases, a feature en- 

 tirely unknown to Link's description and of extremely uncertain value, 

 since by their crowding the sporangia are likely always to be pushed 

 above each other. We therefore regard Chondrioderma stromateum 

 (Link) Rost. as a synonym of the present species, as the original 

 description, so far as it goes, indicates. 



Forms in which the hypothallus is lacking or poorly developed were 

 formerly placed in D. cinereum Morgan, but there is a perfect transi- 

 tion between such forms and the typical phase. 



Widely distributed in North America and Europe. Also reported 

 from Bolivia, Chile; Ceylon, Java, Manchuria, Japan. 



7. DlDERMA CRUSTACEUM Peck 



Rept. N. Y. State Museum 26 : 74. 1874. 

 PI. IX, Figs. 186, 187. 



1888. Chondrioderma crustaceum (Pk.) Berlese, in Sacc, Syll. Fung. 7 : 373. 

 1899. Chondrioderma globosum (Pers.) Rost. ex Lister, Mycetozoa 78, in part. 

 1911. Diderma globosum Pers. ex List., Mycetozoa ed. 2. 104, in part. 



Sporangia closely crowded or superimposed, in a cushion-like colony, 

 creamy white or occasionally pinkish, globose, embedded in the sub- 

 stance of the hypothallus, the outer peridium smooth, delicate, crus- 

 taceous, fragile, remote from the blue iridescent inner membrane; 

 hypothallus prominent; columella variable, generally present, globose; 

 capillitium dark colored, the threads branching and combining to 

 form a loose net; spore-mass black; spores by transmitted light dark 



