288 BOTANICAL GAZETTE [ocTOBER 
but rather to give a diagnosis of the salient and characteristic 
features by which the species is to be recognized. 
KEY TO THE SPECIES 
This key is based on typical specimens. For the determination of inter- 
grading forms, reference should be made to the comparative notes, which 
follow each species. 
em ee eee eee es g. S. albicans 
AA. Plants not chalky-powdery. 
B. Primary thallus present. 
C. Spores 4 wide, ends blunt; podetia os ending in 
a ee AS pileatum 
CC. aie 2.7 Bh aide ends pointed; —— nibs ending in 
S. condensatum 
BB. ae thallus absent. 
C. True squamules absent, — ending in flattened, foliose 
PASS oS a 5 ogi selena = a eee eer 8. S. Wrightit 
CC. True squamules eee 
D. Squamules of the palmate-digitate type (see fig. 7): 
E. Podetia ees or faintly tomentose, cephalodia 
with Stigo 
F Podetia 1 ey branched and spreading 
A S. paschale 
FF. Podetia in ame cushion 
. S. paschale v. conglomeralum 
EE. Podetia more or shes cao tomentose, cephalodia 
with Nostoc. 
F. —— repeatedly carts 
bd _ S. tomentosum 
FF. Podetia ae 
_ S. tomentosum v. simplex 
DD. Squamules of some other fee 
E. Squamules coralline........-+-- a0. 
EE. Squamules umbilicate or coarsely granular 
F. Podetia pabrows, cephalodia with th Some 
coralloides 
udatum 
FF. Podetia tomentose, cephalodi ae Nostoc 
. §. alpinum 
Section PRosTEREOCAULON 
Primary thallus persistent and closely adnate to the saben 
podetia mostly short, under 2 cm., and simple or sparingly branchee; 
