OF WESTERN PENNSYLVANIA. 13 



21. Capsule cernuus, with a long and inflated 



neck; teeth cleft or perforate Trematodon, p. 51 



21. Capsule erect or inclined; neck short or 

 none; teeth cleft to the middle into two 



filiform divisions Dicranella. p. 60 



22. Monoicous; leaves tufted: capsules 

 strumose, costa with distinctly 



heterogeneous tissues '. Oncoplwrus, p. 65 



22. Dioicous; leaves flexuose-spread- 

 ing or secund; capsule more or less 



distinctly strumose 23 



23. Basal auricles of leaves large and in- 

 flated; seta cygneous Dicranodontiuw, p. 72 



23. Basal auricles of leaves small or none; 



seta not cygneous Dicranttm, p. 66 



24. Pe.ristome distinctly twisted; 



teeth 32 25 



24. Peristome not distinctly twisted; 



teeth 16 but often deeply cleft.. 27 



25. Leaves large, oblong to sub-spatulate; 



costa with two median guides Tortilla, p. 103 



25. Leaves small and narrow, linear-lanceo- 

 late: costa with from 4-8 median 



guides 26 



26. Leaf-margins plane, not revolute; 



cells papillose Tortella, p. 95 



26. Leaf-margins revolute. at least be- 

 low; cells smooth or papillose Barbula, p. 97 



27. Dark green or blackish mosses on rocks 

 or sometimes trees: peristome single or 



none 28 



27. Green plants, not blackish nor very 



dark 30 



28. Calyptra descending much below 

 the base of the capsule, split and 



plicate; annulus none: spores large. Glyphomitrium, p. 107 

 28. Calyptra shorter. not plicate; 

 annulus present: spores medium 



size 29 



29. Teeth sub-entire, cribrose or irregularly 



cleft Grimmia. p. 108 



29. Teeth cleft to near the base into fili- 

 form segments Rhacomitrium, p. m 



30. Calyptra mitrate. not folded nor 

 torn, completely covering the cap- 

 sule; capsule erect Hncalypta, p. 105 



30. Calyptra cucullate 31 



31. Teeth merging below into a more or less 

 continuous basal wall or membrane.. 32 

 31. Teeth not merging below into a continu- 

 ous membrane 35 



32. Leaves papillose on the upper sur- 

 face: peristome teeth short Didymodon. p. 96 



32. Leaves mostly smooth: peristome- 



teeth long 33 



33. Capsule inclined, distinctly plicate when 



dry; leaf-cells roundish-quadrate above.. Ceratodon, p. 57 

 33. Capsule erect, nearly or entirely smooth 

 when dry: leaf-cells elongated above. 34 



