OF WESTERN PENNSYLVANIA. 21 



or rounded with an obtuse apex, 

 olive or grayish-green, apex faintly 

 crenulate; cilia three; annulus none. Hypnuni, p. 302 

 117. Alar cells not at all or but very little 



differentiated; plants distantly and ir- 

 regularly pinnate; leaves squarrose or 



spreading-secund Rhytidiadelphus, p. 295 



117. Alar cells distinctly differentiated; plants 



closely pinnate; leaves circinate-secund. . Ctenidium, p. 294 



118. Plants large, to 15 cm., closely and 

 regularly pinnate; leaves linear- 

 acuminate from a broadly ovate 

 base, stem-leaves plicate, falcate- 

 secund; cilia 3 or 4 Ptilinm, />. 303 



118. Plants large to quite slender, simple 

 or pinnate, mostly irregularly 

 pinnate; leaves ovate-to cordate- 

 lanceolate, shortly to slenderly acu- 

 minate, generally circinate-secund 



in two series - . Stcreodon, p. 304 



119. Leaf-cells very narrowly prosenchyma- 



tous, alar cells mostly not differentiated; 



leaves oblong to linear, short pointed, or 



ovate- to linear-lanceolate, acute to 



long acuminate or piliferous hopterygium, p. 316 



119. Leaf-cells not so narrow, alar cells 



broader, hyaline and thin-walled; leaves 



broadly lanceolate to oval, more or less 



long acuminate Plagiothecium, p. 321 



BRACHYTHECIACEAB (120-126) 



120. Capsule practically erect and sym- 

 metric; seta papillose; inner peris- 

 tome much shorter than the outer.. Homalotheciella, p. 330 



120. Capsule generally inclined or hori- 

 zontal, unsymmetric; peristomes of 



equal length 121 



121. Leaves with several deep sulcations Camptothecium, p. 331 



121. Leaves smooth or but shallowly sul- 



cate 122 



122. Operculum conic, sometimes rost- 

 rate; alar cells differentiated Brachytheciuin, p. 332 



122. Operculum long rostrate; alar cells 



few or not differentiated 123 



123. Autoicous; branches and leaves often 



complanate, leaves mostly only slightly 



concave, never sulcate, ovate to ovate — 



lanceolate, more or less long acuminate: 



costa rarely ending in a spine on the back 



of the leaf; cells narrow, smooth; seta 



smooth Rhynchostegium, p. 354 



123. Dioicous; seta generally papillose; costa 



sometimes ending in a spine on the back 



of the leaf 124 



124. Leaves very concave, not at all or 

 but weakly plicate, ovate to oblong, 

 more or less abruptly acuminate or 

 piliferous; costa not ending in a 

 spine; cells narrow and smooth... Cirriphyllum, p. 345 



