OF WESTERN' PENNSYLVANIA. 19 



98. Stems round, creeping, procumbent 

 or more or less erect, often irregu- 

 larly stoloniferous; leaves ascend- 

 ing to appressed, often complanate. 

 rarely secund: stem and branch 

 leaves dissimilar in the stolonifer- 

 ous species only, ovate to lanceo- 

 late, mostly slenderly acuminate; 

 costa not often reaching the apex 

 but usually reaching to the middle 

 at least: cells prosenchymatous, 

 long rhomboidal to linear-vermicu- 

 lar; operctilum conical, blunt to 

 long rostrate 120 [Brachythcciaccae] 



HYPXACEAE (99-119) 



99. Costa in our species single, extending to 

 the middle of the leaf or beyond: opercu- 



lum never rostrate 102 [Amblystegieae] 



99. Costa double and short or none: opercu- 



lum sometimes rostrate 100 



100. Stem and branch leaves usually dis- 

 tinctly dissimilar: leaves symmetric, 

 inserted at right angles to the axis 



of the stem 114 [ Hyhcomieae] 



100. Stem and branch leaves quite 

 similar: leaves often inserted 

 obliquely and un symmetrically.. 101 

 101. Leaves either symmetric and normally in- 

 serted or un symmetric and obliquely in- 

 serted; operculum sometimes rostrate. 118 [Stereodonteae] 

 101. Leaves obliquely inserted, apparently 

 two-ranked. mostly unsymmetric; 

 branches mostly complanate; operculum 

 conic to short rostrate, rarely long- 

 rostrate ' . . . . 119 [Plagiothecieae] 



102. Leaves margined Sciaromium, p. 279 



102. Leaves not margined 103 



103. Costa strong, ending almost in the apex 



or sometimes excurrent 104 



103. Costa not extending to the apex of the 



leaf . 109 



104. Paraphyllia numerous and poly- 

 morphic 105 



104. Paraphyllia none or very few... 106 

 105. Leaves deeply longitudinally folded. 



falcate-secund ( Cratonenron} 



105. Leaves not deeply longitudinally folded.. Hygroamblystegium,p.275 



106. Leaf-cells linear-vermicular to the 



leaf-base, mostly with blunt ends, 



the alar cells forming a small but 



well defined group of quadrate or 



rectangular cells Hygroliytwuin. f>. 287 



106. Leaf-cells hexagonal and 2 to 6 

 times as long as wide, or prolonged- 

 linear and becoming wider and 

 shorter towards the leaf-base, alar 

 cells forming a larger group often 

 reaching to the costa 



