OF WESTERN PENNSYLVANIA 89 



i;. Both surfaces of the teeth equally well-developed and no pro- 

 jecting plates. f. 

 f. Pericha;tial leaves long-convolute-sheathing. 



8. Barbula. 

 f. Perichastial leaves not or but little convolute-sheathing. 



g. 

 g. Leaves more or less Ungulate, margins plane; cells smooth. 



7. Didy-modon. 

 g. Leaves more or less lanceolate. i. 



i. Leaf-margins plane or involute; cells papillose. 



i. Leaf-margins more or less revolute; leaf-cells nearly smooth 

 or papillose. k. 



i. Divisions of peristome erect or slightly dextrorsely twisted. 



5. Trichostomum. 

 j. Divisions of peristome distinctly sinistrorsely twisted. 



6. Tortclla. 



k. Peristome-teeth 16, more or less 2-cleft or perforate, erect or 



dextrorsely ascending. 7. Didymodon. 



k. Peristome-teeth 32, filiform, strongly twisted sinistrorsely. 



8. Barbula. 

 1. Cleistocarpous; capsule spherical to oval, apiculate. 



9. Phascum. 

 1. Operculate. m. 



m. Peristome-teeth 16. n. 



m. Peristome-teeth 32, filiform, sinistrorsely twisted, with a high 

 basal membrnae. 12. Tortula. 



n. Peristome-teeth none, or rudimentary from a low basal membrane. 



10. Pottia. 



n. Peristome-teeth small, separate to the base, more or less divided 

 into two slender prongs. 11. Desmatodon 



I. ASTOMUM Hampe. 



Autoicous, rarely polyoicous : small, gregarious to cespi- 

 tose, dull green : stem with a few-celled central strand, radicu- 

 lose, thickly foliate ; upper leaves tufted, when dry mostly 

 crisped, keeled, from a broad base lanceolate to subulate- 

 lanceolate, margin plane to involute, entire ; costa strong, per- 

 current or excurrent ; leaf-cells in upper part of leaf small, 

 rounded-quadrate, piapillose both sides, the lower cells 

 elongate-quadrangular, thin-walled and hyaline : capsule most- 

 ly immersed, almost spherical to oblong-elliptic, mostly with a 

 small, elongate-conic operculum, which, however, is rarely 

 deciduous ; calyptra cucullate, rarely mitrate, smooth. 



A widely distributed genus of 21 terrestrial species; 5 

 species occurring in North America ; 3 species in our region. 

 Key to the Species. 



a. Leaves crisped when dry. b. 



a. Leaves not crisped when dry; capsule castaneous, ovoid. 



3. A. nitidulum. 

 b. Capsule brown, globose; spores usually .014-.017 (rarely 

 .020) mm. in diameter, mature in spring. 



1. A, crispum. 



b. Capsule brownish to orange, sub-globose; spores usually .021- 

 .027 mm., ripe from late autumn to early spring. 



2. A. sulKvantU. 



