580 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 
Rhizome scales larger, variously shaped (never roundish), 
with long-acuminate to subacicular tips, straight 
to oblique or subsquarrose, very widely imbricate. 
Fronds distant, the rhizome relatively slender and 
wide-creeping. 
Sori impressed, the upper surface of the segment 
strongly embossed. 
Fronds large, short-stipitate; segments mostly 
long-acuminate; sori medial, up to 2.5 
mm, broad................2.20222-2. 
Fronds much smaller, long-stipitate; seg- 
ments rounded-obtuse; sori supra- 
medial, appearing submarginal, very 
much smaller... ..2........2.2..... 
Sori superficial or nearly so.............-....... 
Fronds subfasciculate or, if somewhat apart, the rhi- 
zome (nos. 6 and 8 excepted) short-creeping 
and relatively very thick. 
Rhizome scales light brown or grayish, often with 
a sharply defined fuscous median area. 
Lamina bearing numerous contiguous or 
slightly imbricate, minutely denticu- 
late scales beneath.................. 
Lamina densely covered beneath with wide- 
ly imbricate, fimbriate scales. 
Segments oblique, widely joined; dark 
stripes of rhizome scales nearly 
percurrent.......2.....0....0.. 
Segments spreading, narrowly joined: 
dark median area of rhizome 
scales basal only............2.... 
Rhizome scales dark castaneous to ferruginous, 
never sharply bicolorous. 
Pinne distant, membranous, often bipartite 
or tripartite...........0000022.00000. 
Pinne (segments) much closer, herbaceous 
to coriaceous, simple. 
Fronds long-stipitate; lamina suborbi- 
cular to ovate-oval............... 
Fronds mostly very  short-stipitate; 
lamina narrowly linear to linear- 
oblong. 
Lamina gradually long-attenuate in 
the basal half, many pairs of 
lower segments minute or even 
vestigial. 
Rhizome scales flaccid, mostly 4 
to 7 mm. long, broadly linear- 
attenuate from a= slightly 
broader base.........2..... 
Rhizome scales more rigid, 2 to 
3.5 mm. long, relatively 
broader at the base. 
4. P. macrolepis. 
5. P. polypodioides. 
P. thyssanole pis, 
7. P. argentinum, 
8. P. leucosporum. 
6. P. thyssanolepts, 
9. P. tridens, 
10. P. lepidotrichum. 
11. P. leptdopteris, 
