OF WESTERN PENNSYLVANIA. 15 



51. Annulus present; leaf-cells narrowly 

 rhombic to linear: leaves green to yel- 

 low-green, often glossy JVebera, p. 140 



52. Rock- or crevice-inhabiting 



mosses 53 



52. Earth-inhabiting plants 58 



53. Leaves on the sterile stems in two rows, 



forming a continuous marginal wing... Scliistostega, p. 137 

 53. Leaves on the sterile stem not thus ar- 

 ranged 54 



54. Leaves distichous, closely imbri- 

 cate, carinate-plicate; stems radicu- 



lose and bulbiform at base Bryo.viphinm, p. 78 



54. Leaves not as above; stem not 



bnlbiferous at base 55 



55. Leaves ecostate; stalk less than 1 mm. 



long; operculum apiculate .-. . Hedivigia, p. 201 



55. Leaves costate; stalk 2 to 12 mm. long; 



operculum rostrate 56 



56. Capsule smooth, terminating the 

 main axis; plants often on calcare- 

 ous rocks 57 



56. Capsule ribbed, borne on a short 

 lateral branch; plants not often on 



calcareous rocks Amphidium, />; 114 



57. Leaf-margins revolute on one or both 

 sides; upper leaf-cells clear and pellucid; 

 columella remaining attached to the 



operculum and falling away with it Hymcnostylhtm, p. 92 



57. Leaf-margins always plane; upper leaf- 

 cells densely papillose and obscure; 

 columella remaining in the capsule after 



the operculum falls away Gymnostomum, p. 92 



58. Calyptra cucullate: cells iso-dia- 



metric above the middle of the leaf Pottla, p. 101 

 58. Calyptra mitrate; cells elongated 



above the middle of the leaf 59 



59. Capsule immersed and sessile, splitting 

 equatorially and without specially modi- 

 fied cells at the line of dehiscence Aphanorhegma, p. 131 



59. Capsule exserted on a long seta, or, if 

 immersed, operculate with 13 rows of 



denser cells below the line of dehiscence. Physcomitriuni. p. l$2 

 60. Capsule symmetric; peristome 



single 61 



60. Capsule unsymmetric; peristome 

 double, the inner in the form of a 



short conical tube 64 



61. Peristome teeth 4 Tetraphis, p. 184 



61. Peristome teeth 32 or 64 62 



62. Capsule usually square or hexa- 

 gonal: calyptra densely hairy: teeth 



generally 64 Polytrichum, p. 194 



62. Capsule cylindrical; teeth 32... 63 

 63. Calyptra densely hairy: leaves not 



crisped when dry Pogonatum, p. 192 



63. Calyptra cucullate, almost smooth: leaves 



crisped when dry Catharin&ea, p. 186 



64. Leaves green, costate. conspicuous; 



capsule sessile and immersed Diphyscimn, p. 



