28 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 
that additional species will be found, on the continent, from Mexico 
southward; and it is sincerely to be hoped that further collections 
may be made in the humid districts of eastern and southern Mexico 
to bring to light complete material of those known at present only 
from the original collections. 
KEY TO THE NORTH AMERICAN SPECIES.! 
Veins mostly free, only very rarely forming basal arches along 
the costa. 
Pinne varying from entire or slightly repand to crenate. 
Texture thin; veins not strongly elevated; sori extend- 
ing half way to the midvein of the pinne...... 1. H. speciosa. 
Texture coriaceous; veins strongly raised beneath; sori 
in submarginal lines on shallow scallops. ........ 2. 7. integrifolia. 
Pinne cut from one-third to completely to the costa. 
Segments obtuse or distinctly rounded (rarely acute in 
no. 8). 
Sori submarginal......222220.0.0020002.222....... 3. H. bella. 
Sori borne distinctly apart from the margin, varying 
from supramedial to inframedial. 
Pinne pinnately cut about halfway to the 
costa; veins simple (those on the distal 
side of the segments usually so), or once- 
forked..........2.2.0.20.20000.020220-- 4. H. contigua. 
Pinnx deeply pinnatifid, two-thirds or nearly 
to the costa; all but the outer veins of 
the segments once or twice-forked. 
Segments oblong or deltoid-oblong, rela- 
tively broad; veins 10 to 14 pairs. 
Pinnz oblong-linear, 30 to 35 cm. long, 
4 to 5.5 cm. broad, relatively 
short-acuminate; segments 10 
to 12 mm. broad at the sinuses, 
strongly arcuate toward their 
apices... ......2..2.22..2..... 5. A. pittieri. 
Pinnz oblong-lanceolate, 18 to 25 cm. 
long, 3.2 to 3.8 em. broad, the 
apex gradually long-acuminate; 
segments 7 to 9 mm. broad at 
the sinuses, slightly or not at 
all arcuate. .........200..2.... 6. 1. chiricana. 
Segments narrowly oblong; veins 14 to 23 
pairs; pinne much more deeply 
pinnatifid. 
Veins 14 to 17 pairs, the branches dis- 
tant and divergent; sori medial. 7. H. arachnoidea. 
Veins 19 to 23 pairs, the branches very 
close and diverging at a very 
acute angle; sori distinctly in- 
framedial, crowded............ 8. H. mutica. 
i, 71 
' For the sake of comparison or for the purpose of explaining taxonomic confusion 
there are included in the present treatment several species which are not known to 
occur in North America, including Panama. 
