OF WESTERN PENNSYLVANIA 263 



c. Leaves either symmetric and normally inserted or unsymmetric 

 and obliquely inserted; lid sometimes rostrate. 



s. (Stcrcodonteac). 



c. Leaves obliquely inserted and apparently two-ranked, mostly un- 

 symmetric; branches mostly complanate; lid conic to short- 

 rostrate, rarely long-rostrate. t. (Plagiothccieac}. 

 d. Leaves bordered. S. Sciaromhun. 

 d. Leaves non-bordered. e. 



e. Costa strong, sub-percurrent, or sometimes excurrent. 



f. 

 c. Costa not reaching leaf-apex. j. 



f. Paraphyllia numerous, polymorphic; leaves non-plicate. 



4. Hygroamblystegium. 



f. Paraphyllia none or scarce. g. 



g. Leaf-cells linear-vermicular to the leaf-base, mostly with blunt 

 ends, alar cells forming a small, distinct, well-defined group of 

 quadrate or rectangular cells. 9. Hygrohypnum. 



g. Leaf-cells hexagonal and 2-6-times as long as wide, or prolonged- 

 linear and becoming wider and shorter basally, alar cells forming 

 a group which is large and often extends to the costa. 



h. 

 h. Alar cells parenchymatous. 6. Drepanocladus. 



h. Alar cells prosenchymatous. i. 



i. Leaf-cells prolonged-linear. 7. Calliergon. 



i. Leaf-cells prosenchymatous-hexagonal, 2-6 times as long as wide. 



4. Hygroamblystegium. 



j. Leaves cordate to ovate-lanceolate, acuminate; costa weak, 

 reaching the middle of leaf or beyond; leaf-cells rarely linear, 

 mostly parenchymatous and 4-sided or prosenchymatous and 6- 

 sided. 1. Amblystcgium. 



]. Characters not combined as above. k. 



k. Leaf-cells narrowly linear: leaves broadly ovate or cordate, with 

 reflexed-squarrose and subulate-acuminate tips. 



10. Campylium. 

 k. Leaf-cells and leaves not as above. 1. 



1. Leaves oval to oblong-lanceolate, long-acuminate; cells narrow- 

 ly prosenchymatous; plants shining. 3. Homomallium. 

 1. Not as above. m. 



m. Slender, dull; leaves spreading, lanceolate to lance-linear; cells 

 rhomboidal to long-hexagonal, 2-6 or rarely 6-8 times as long as 

 broad. 2. Amblystcgiella. 



m. Leaf-cells prolonged-linear, mostly very narrow. 



n. 



n. Leaves erect-spreading to imbricated, oblong-ovate to rounded, 

 obtuse or apiculate, often deeply concave; costa short and 

 double or none. 8. Acrocladium. 



n. Leaves more or less falcate-secund to circinate, from a mostly 

 narrowed and somewhat decurrent base becoming ovate- to 

 triangular- or cordate-lanceolate, more or less slenderly acumi- 

 nate, costa weak, reaching about to leaf-middle or even in some 

 cases excurrent. 6. Drepanocladus. 



o. Paraphyllia numerous; leaves more or less erect, from abruptly 



to shortly acuminate, mostly plicate. 14. Hylocomium. 



o. Paraphyllia none or very few. p. 



p. Stem-leaves more or less sqnarrose-spreading to secund, 



acuminate. r. 



p. Stem-leaves more or less crowded, imbricate, but with more or 

 less spreading to secund tips. q. 



