MAXON—STUDIES OF TROPICAL AMERICAN FERNS. 548 
might with some justice be added to the group of P. myosuroides, 
treated in a former paper,’ which they resemble in their rhizome 
scales, simple veins, and elongate sori. The whole series of species 
is of unusual interest from the fact that the individual unit charac- 
ters (which are stated at length in the key) are variously combined 
in the different species. The points of specific difference are exact 
rather than comparative and so, with one or two exceptions noted 
in the text, the status of the species is fairly certain. Several of the 
species—e. g., P. cookii, P. williamsii, P. basiattenuatum, P. tri- 
chomanoides, P. serricula, and P. setuloswum—have bifurcate or 
branched glandular hairs upon one or both sides of the lamina, 
the terminal cells being enlarged and more or less clavate. No 
examples of this structure in other families are known to the writer. 
KEY TO THE SPECIES. 
Veins of all the segments simple. 
Scales of the rhizome not ciliate. 
Lamina slightly pubescent, or, if subsetulose the 
hairs mostly short, brittle, or caducous. 
Segments minute, very oblique, long-decur- 
TON. .ceeececece eee e eee eeeeees . 1. P. micropteris. 
Segments larger, spreading, not long- decur- 
rent. 
Scales of the rhizome 0.6 to 1 mm. long, 
elongate-deltoid to ovate, acumi- 
nate to acutish, attached far above 
their base, the outermost 1 or 2 
rows of cells minute and relatively 
thin-walled.............-------- 2. P. limula, 
Scales of the rhizome 1 to 3 mm. long, 
lance-linear to lance-oblong, at- 
tached at or near their base, not 
bordered by conspicuously smaller 
cells. 
Segments narrowly oblong; scales 
mostly 8 to 12 cells broad, 
clathrate, the cells subquad- 
rate to broadly oblong. ....-- 3. P. hartit. 
Segments deltoid-oblong; scales 13 to 
20 cells broad, the cells mostly 
elongate - hexagonal, much 
smaller........---------+---+ 4. P. nutatun.. 
Lamina conspicuously bristly-setose, the hairs 
long and persistent. 
Plants of coarse aspect, the stipe 0.5 mm 
thick; lamina merely pinnatified, the 
segments coarse and rather broadly 
joined...............----+-+-+-++-+-- 5. P. cookit. 
1 Contr. U. §. Nat. Herb. 17: 398-406. pls. 11, 12. 1913. 
