270 American Midland Naturalist Monograph No. 6 



almost symmetric or weakly gibbous, when dry only rarely arcuate and nar- 

 rowed below the mouth, mostly smooth; annulu5 present or none; peristome- 

 teeth basally confluent, subulate, yellowish, mostly hyaline-bordered, with 

 divisural zigzag, cross-striate, apically hvaline and papillose, lamellae numer- 

 ous; cilia 1-2, nodose, rarely 3 and appcndiculate; lid conic-convex, sometimes 

 tostrate. 



A genus of world-wide distribution and containing about 170 species, most- 

 ly occurring on decaying wood; about 25 species reported for North America; 

 about 7 species in our region. 



Key to the Species* 



A. Leaves entire or only obscurely serrulate at apex B 



A. Leaves usually distinctly serrate or serrulate at least in upper half E 



B. Leaves perfectly entire C 



B. Leaves obscurely serrulate at apex D 



C. Cells about .005-.008 x .075-.160 mm, about two rows at the base shorter and sub- 

 oval; cortical stem-cells not enlarged and hyaline 5. /. pulchellum 



C. Cells about .003-.005 x .080-.100 mm, hardly different at base; cortical cells of stem 



enlarged and hyaline 1. /. Muellerianum 



D. Alar cells few, quadrate, forming a small group 6. /. micans 



D. Alar cells very mdistinctly sub-rectangular, not forming a well defined group 



2. /. elegans 



D. See also /. pulchellum var. nitidulum 

 E. Leaves shortly bi-costate; annulus large and compound; leaf-cells papillose by pro- 

 truding cell angles 4. /. geophilum 



E. Leaves ecostate or obsoletely costate F 



F. Leaves serrulate to the base or nearly so G 



F. Leaves not serrulate below the middle /. micans 



G. Operculum conic; leaf-cells not papillose dorsally towards leaf-apex; leaves compla- 



nately spreading 7. /. turfaceum 



G. Operculum short-rostrate; leaves closely complanately overlapping 3. /. deplanatum 



1. Isopterygium Muellerianum (Schimper) Lindberg 



(Plagiothecium Muellerianum Schimper) 



Yellowish-green, laxly cespitose; the branches long, flattened, straggling 

 out into flagella or stolons or forming flattened 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 p)oints directed forwards and upwards so that the 

 dorsal surface of the branch is concave, lance-ovate, 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, cistaneous; capsule smooth, small, long-necked, obovoid, erect to 

 inclined, when dry pale brown, wide-mouthed and campanulate; lid conical, 



''' Also /. subfalcatum Austin, with sub-cultirform leaves turned backwords, non-decur- 

 rent, apically serrate. In cracks and crevices of rocks, Pennsylvania to New England. 

 See Sullivant's Icones Muscorum. Supplement, plate 67. 



