92 THE NORTH AMERICAN SLIME-MOULDS 



IO. DlDYMIUM EXIMIUM Peck. 



PLATE XVI., Fig. 9. 

 1879. Didymium eximium Peck, Rep. N. Y. Mus., XXXI., p. 41. 



Sporangia scattered, dull grayish yellow or gray, globose, um- 

 bilicate, minute, stipitate ; the peridium comparatively thick, 

 tenacious, especially persistent below, tawny or yellow ; the 

 stipe pale brown or orange, erect, even or slightly enlarged at 

 base ; hypothallus scant or none ; columella prominent, more or 

 less discoidal, rough, or spinulose, especially on the upper sur- 

 face, yellow ; capillitium not abundant, pale fuliginous, often 

 branching and anastomosing so as to form a loose net ; spores 

 nearly smooth, dark violaceous by transmitted light, 8.5-9.5^. 



Apparently rare. All our material is from Dr. Rex, and all 

 collected in New York, Adirondack Mountains. The species 

 differs from D. xanthopns in several particulars, - - in the much 

 firmer, more persistent, and less calcareous peridium, in the 

 more complex capillitium, in the darker and larger spores, and 

 especially in the peculiar and prominent columella, which is not 

 only rough, but even " sometimes spinulose even to the extent 

 of long spicules penetrating to one-third the height of the 

 sporangia." N. A. F., 2493. 



3. Diderma Persoon. 



1794. Diderma Persoon in Roem. N. Mag. Bot., I., p. 89. 

 1873. Chondrioderma Rost. Versuch, p. 13. 



Sporangia plasmodiocarpous or distinct, sessile or stipitate ; 

 the peridium as a rule double, the outer wall generally calcare- 

 ous with the lime granules globular, non-crystalline, the inner 

 wall very delicate and often, in the mature fructification, remote 

 from the outer ; columella generally prominent. 



The genus Diderma is usually easy of recognition, by reason 

 of its double wall, the outer, crustaceous, usually calcareous, and 

 its limits remain substantially as originally set by Persoon. His 

 definition is as follows : 



