OF Western Pennsylvania 317 



annultis present or none; peristome-teeth basallj cotlfliient, 

 subulate, yellowish, mostly hyalifle-bordered, -with clivisural 

 zigzag, cross-striate, apically hyaline and papillose, laiiiellse 

 numerous ; cilia 1^2, ftodo'se, rarely 3 and appendiculate ; lid 

 c6nic-convex, sometimes rostrate. 



A genus of world-wide distribution and containing about 

 170 species, mostly occurring on decaying wood; about 25 

 species in North America ; about 7 species in our region. 



Key to the Species. 

 a. Leaves entire or obscurely serrulate at apex. 



b. 

 a. Leaves distinctly serrulate at least in upper half, 

 b. Leaves perfectly entire. c. 



b. Leaves obscurely serrulate at apex. d. 

 c. Cells about .0OS-.008x.075-.160 mm., about two rows at the base 

 shorter and sub-oval. 5. /. pulcheltum var. 



c. Cells about .003-.00SX-080-.100 mm., hardly dififerent at' base. 



1. /. muellerianum. 

 d. Alar cells few, quadrate, forming a small group. 



6. /. micans. 

 d. Alar cells very indistinctly sub-rectangular. 



2. /. elegans. 

 e. Leaves shortly bi-costate; annulus large and compoiind. 



4. /. geophilum. 

 ■e Leaves ecostate or obsoletely costate. f. 



f. Leaves serrulate to the base. 3. /. deplanatum. 



f. Leaves not serrulate below the middle. 7. /. turfaceum. 



1. Isopterygium muellerianum (Schimper) Lindberg. 



{Plagiothecium muellerianum Schimper). 



Yellowish-green, laxly cespitose ; the branches long, flat- 

 tened, straggling out into flagella or stolons or forming flat- 

 tened strands, very slender; the stems and branches thick, 

 often more than .150 mm. in diameter, with very large and 

 thin-walled outer cells which are 3 or 4 times as wide as the 

 lower cells of the leaf and usually about .015-025 mm. wide; 

 leaves rigid, not much different when dry, the points directed 

 forwards and upwards so that the dorsal surface of the branch 

 is concave, lance-ovate, abruptly long-apiculate, concave, non- 

 decurrent, plane-margined, entire ; costa double, very faint and 

 short; median cells linear, narrow, up to .100 mm. long, about 

 20-25:1, the alar and basal scarcely different; perichaetial 

 leaves ovate-oblong, acuminate, entire: seta rather short, 

 castaneous ; capsule smooth, small, long-necked, obovate, erect 

 to inclined, when dry pale brown, wide-mouthed and campanu- 

 late; lid conical, rostellate; peristome-teeth with rather dis- 

 tant articulations, cilia short and unequal ; annultis 1-seriate ; 

 spores mature in autumn ; dioicous. 



On moist earth and rocks in ravines, etc., mostly in hilly 

 or mountainous regions ; Europe, Asia, and from New England 



