OF WESTERN PENNSYLVANIA. 49 



Family II. DICRANACEAB. 



Autoicous or dioicons ; large to minttte, mostly cespitose: 

 stem with a central strand, often thickly covered with rhizoids, 

 mostly densely leafy, branched; leaves often falcate-secund, 

 mostly acuminate to narrowly linear from a broader base, 

 usually more or less smooth and shining, usually costate ; costa 

 f ometimes dorsally serrate, heterogenous ; leaf-cells sometimes 

 mammillate, the basal ones enlarged and mostly transparent, 

 alar cells often much larger and either hyaline or brownish, 

 the central leaf-cells short to rounded, mostly smooth ; 

 perichaetial leaves often sheathing : seta usually erect and long ; 

 capsule mostly unsymmetric, usually c^rnuous, when dry often 

 curved and sulcate ; annulus present or absent ; peristome 

 simple or rarely none; when present the peristome teeth are 

 16 in nvimber, approximate, united below into a basal mem- 

 brane, usually two-parted to the middle, or beyond, into linear 

 or awl-like divisions, no longitudinal lines, but the teeth 

 minutely striate or papillose on the dorsal face, rarely smooth, 

 inner face yellow with one or two longitudinal lines and with 

 more or less projecting trabecule; operculum more or less 

 long-rostrate ; calyptra usually cucullate. 



Key to the Genera. 



a. Cells of costa in. cross-section homogeneous; peristome-teeth 

 broad, flat, undivided, mostly smooth, rarely none. 



6. Seligeria. 



a. Cells of costa as seen in cross-section heterogeneous; teeth nar- 

 row, prolonged, mostly two-parted, striate or papillose. 



b. 

 b. Alar cells not differentiated. i. Bruchia. 



h. Alar cells differentiated. c. 



c. Cells of the lamina smooth. d. 



c. Cells of the lamina mamillate on the free surfaces. 



d. Capsule mostly long-necked; stomata numerous in the neck 



or in middle of capsule-wall. e. 



d. Capsule with a short neck or none; stomata few or none. 



g. 

 e. Calyptra mitrate; operculum either not deciduous or else not dif- 

 ferentiated, f- 

 e. Calyptra cucullate; operculum deciduous. 2. Trcmatodon. 

 f. Capsule immersed, erect, without a neck, apiculate. 



(Sporledera) 

 i. Capsule immersed or slightly exserted, with a distinct neck, 

 more or less cernuous, rostrate. I. Bnichia. 



g. Capsule mostly unsymmetric, not erect. 7. Dicranclla. 

 g. Capsule symmetric and erect. h. 



h. Operculum not differentiated. 3. Plctiridiuui. 



h. Operculum differentiated. i. 



i. Upper areolation rounded-quadrate: capsule plicate or furrowed. 



nor plicate. 4- Ditrichum 



i. Upper areolation more or less elongate: capsule neither furrowed 

 nor plicate. S- Ceratodon. 



