100 OUR NATIVE FERXS AXD THEIR ALLIES. 



10. P. ornithopus Hook. Stipes tufted, 3' 8' long, 

 rather stout, dark-brown; fronds very rigid, 3' 12' long, 2 3' 

 broad, broadly deltoid-lanceolate, bi tripinnate ; primary pin- 

 nae spreading or obliquely ascending, linear, bearing 4 16 pairs 

 of trifoliate (varying from simple to 5 7 foliate) mucronulate 

 pinnules, li" 2" long ; margins inflexed to midrib in fertile 

 fronds. (Allosorus mucronatus D. C. Eaton.) California. 



11. P. Wrightiana Hook. Rootstock short, thick, densely 

 chaffy; stipes crowded, purplish-brown, 4' 6' long; fronds 

 3' 10' long, i' 3' broad, lanceolate to deltoid, trifoliate at apex, 

 bipinnate below ; pinnae short with i 2 pairs of long narrow 

 pinnules besides the terminal one; mucro short, with margin 

 broad and cartilaginous ; margins of fertile fronds inflexed to 

 the midrib. Very variable; forms with fronds decreasing to 

 simply pinnate at the apex, and longer but less broadly winged 

 mucro form var. longimucronata Dav. (P. longimucronata 

 Hook.); forms with pinnules densely crowded are var. compacta 

 Dav. Colorado and Texas to California. 



12. P. densa (Brack.) Hook. Rootstock slender, chaffy 

 with blackish scales ; stipes densely tufted, wiry, very slender, 

 castaneous, 3 9' long; fronds ovate or triangular-oblong, 

 i' 3' long, densely tripinnate; segments 3" 6" long, linear, 

 nearly sessile, sharp pointed or mucronate, in the fertile fronds 

 entire, with the margin narrowly recurved ; in the rare sterile 

 fronds sharply serrate, especially toward the apices, (pnych- 

 ium densuin Brack.) Utah (Jones), and Wyoming to California, 

 Oregon, and northward ; Mt. Albert, Gaspe, Quebec (Allen). 



3. PLATYLOMA J. Sm., Baker. Texture coriaceous, the veins 

 usually hidden, the ultimate segments broad and flat, the indusium 

 so narrow as to be soon hidden by the fruit. 



13. P. Bridgesii Hook. Stipes 2' 6' long, tufted, castane- 

 ous ; fronds 4' 6' long, i' or more broad, simply pinnate ; pinnae 

 5 18 pairs, mainly opposite, nearly sessile, glaucous green, 

 coriaceous, rounded or cordate at the base*; indusium narrow, 

 formed of the whitish margin of the pinna, soon flattened out 

 exposing the broad sorus. California. 



14. P. f lexuosa (Kaulf.) Link. Rootstock creeping, slender ; 

 stipes reddish, passing into a more or less flexuous or zigzag 



