PAPERS ON BOTANY A yp 
Dimeriopsis gen, nov. Fig. 2 
This genus of the Dimerineae is characterized by the devel- 
opment of the perithecia below a mycelial skin. Type D.  ar- 
throstylidicola, 
Dimeriopsis arthrostylidicola sp. noy. Fig. 2. 
Spots black consisting of superficial mycelium encircling the 
stems, 0.5 to 2 » long. Mycelium coarse, 4-5 p», somewhat 
c1ooked, brown, densely interwoven and matted in older por- 
tions, at edges 1adiate. Hyphopodia none. Setae 312 » long 
by 10 # thick, thick-walled, numerous on older mycelium. Per- 
ithecia 400-450 » in diameter developed below the mycelial 
layer, sides and top well developed, of brown hyphae, base ex- 
tremely thin, hyaline. Ostiole none. Asci numerous, 100-150x 
25-30 mw, clavate, thick-walled, with a thin spot at the apex, 8- 
spored. Paraphyses present, filamentous, matted, zelatinizing. 
Spores straight to slightly falcate, inordinate, 2-celled, rarely 
4-celled, dark brown, constricted at septa, 12-14x40-55 p» obtuse. 
On Arthrostylidium sarmentosum. Monte Alegrillo, 4772 
(type). 
Fig. 2. Dimeriopsis arthrostylidicola (a) Tip of an ascus showing spores 
and the apical thin spot. (b) Spores showing the constriction at the 
septa, 4772. Drawn by J. MaclInnes. 
This fungus, clearly Perisporiaceous, in its superficial mycel- 
ium, and general characters falls within the Dimerineae,’ and 
close to Dimerium. From this genus, however, it differs rad- 
ically in charcater of the perithecium, very large size and pe- 
culiar shape of spores and the presence of abundant paraphyses, 
The most striking feature is that the perithecia develop below 
the mycelium, i. e., the mycelium over a considerable area 
coalesces to form a continuous black skin which is, however, 
only one layer thick; and below this skin in a partially de- 
1. Theissen, Bot. Cent. 29:46. °” 
