128 American Midland Naturalist Monograph No. 6 



at base, mostly bordered, entire or toothed towards the apex; costa mostly 

 strong, often excurrent, projecting dorsally, provided with median guides; 

 leaf-cells mostly rhombic- to rhomboid-hexagonal, the basal parenchymatous, 

 quadrate to elongate-rectangular; perichaetial leaves narrower and smaller 

 inside: seta long, reddish to brown, hooked or arcuate at apex, capsule cernu- 

 ous to pendent, rarely horizontal, the collum distinct, pyriform to cylindric, 

 rarely ovoid to globose, symmetric to slightly curved, the curve sometimes 

 being entirely in the collum, phaneropore, annulus present, large-celled, plur- 

 iseriate, revoluble; the two peristomes of nearly equal length, teeth confluent 

 at their insertion, lanceolate to linear-subulate, often abruptly narrowed above 

 the middle, yellowish to orange, often hyaline at apex and sometimes with a 

 hyaline border, dorsally minutely papillose, trabeculae sometimes united by 

 cross-partitions; segments mostly free, basal membrane usually high, outwardly 

 carinate, segments narrowly linear to lanceolate-subulate, split along the keel 

 and more or less fenestrate or gaping, rarely entire; cilia filiform, rarely short 

 or lacking, often appendiculate; spores .010-. 050 mm; operculum conic to con- 

 vex-umbonate or rarely quite apiculate. 



A large and difficult genus of about 800 species, of wide distribution; about 

 175 species in North America, of which there are 9 or 10 species in our 

 general range. 



Key to the Species 



A. Leaves usually distinctly bordertd B 



A. Leaves not distinctly bordered, at least not above I 



B. Costa vanishing below the apex H 



B. Costa percurrent to excurrent C 



C. Leaves short- to long-decurrent; costa short-excurrent; synoicous or dioicous 



8. B. bimum (and 7 B. pseudotriquetrum) 



c. Leaves not or but slightly decurrent D 



D. Costa fsercurrent to short-excurrent K 



D. Costa long-excurrent E 



E. Peristome-teeth with the "trabeculae connected by various cross partitions 



L B. angustirete 



E. Peristome-teeth not so connected f 



F. Dioicous G 



F. Synoicous 4. B. cusp-datum 



F. Mostly autoicous; antheridia at ap)ex of lateral innovations 5. B. pallescens 



G. Leaves ovate-lanceolate, with rhomboidal cells 6. B. caespiticium 



G. Leaves rounded to widely ovate; cells short-hexagonal 11. B. cap Hare 



H. Leaves blunt at apex 3. B. tortifolium 



H. Leaves short-acuminate, cuspidate 11. B. capillare 



1. Costa long-excurrent 4. B. cuspidatum 



I. Costa vanishing below middle of leaf; foliage usually white or silvery 



10. B. argenteum 



K. Cilia none, or short and coherent 2. B. uliginosum 



K. Cilia well developed, appendiculate 9. B. bicolor 



1. Bryum angustirete Kindberg 



(B. pendulum Schimper; B. cernuum Bryologia Europaea) 

 Plate XXII 

 Densely cespitose, usually darkish-green: stems in our region short, about 

 6-9 mm, erect, sparsely branched, matted below with a castaneous tomentum, 



