Jennings: Manual of Mosses — 31. Hypnaceae 277 



carinately gaping, the basal membrane about one-third as high, the cilia very 

 slender, about as long as the segments, nodose, usually 3 in number; exothecial 

 cells moderately incrassate, small and quadrate at rim, larger and oblong- 

 rectangular, to rounded-hexagonal below; annulus large, revoluble, 2-seriate; 

 spores pale yellowish, smooth, rather thin-walled, .006-. 010 mm, mature in 

 mid-summer. 



On humus, rocks, rotten logs, etc., in woods; Europe, Asia, northern 

 Africa, and from southern Canada to Alabama and from Alaska to Oregon. 



Known from Allegheny, Armstrong, Butler, Crawford, Erie, McKean, Washington, 

 and Westmoreland counties. With the exception of the McKean County station these 

 records are all from the western part of our region and seem to indicate that this species 

 is at least not common in the? mountains and plateau counties. Specimen figured: Wild- 

 wood Hollow, Allegheny County. June 11. 1908. 



4. Plagiothecium denticulatum [Linnaeus] Bryologia Europaea 

 (Hypnum denticulatum Linnaeus) 



Plate LIII 



Variable, in flattened tufts of a pale and lustrous green, moderately robust, 

 the more or less ascending and elongate branches complanate; leaves rather 

 close, complanate and sub-distichous, rather spreading, when dry little changed, 

 glossy, 2-3 mm long, sub-concave, oval to lance-oblong, shortly and sometimes 

 almost apiculately acute, usually slightly denticulate at the apex, the lower 

 margins entire and often narrowly recurved, the base narrowed to a rather wide 

 and strongly decurrent insertion; costa thin, variable, usually short and double, 

 sometimes forked and reaching almost to the middle, sometimes none; median 

 leaf-cells rhomboid-hexagonal, rather large, about 10-15:1, about .010-015 mm 

 wide, thin-walled, chlorophyllose, gradually becoming laxer, pellucid, and more 

 or less rectangular at base, the alar more hyaline, sub-rectangular, sub-inflated, 

 and still somewhat larger but not forming clearly differentiated auricles, strong- 

 ly decurrent; the apical leaf-cells much smaller, incrassate, rhomboid: seta 

 about 2.5-4 cm long, flexuous, dextrorse above when dry, slender; capsule-um 

 about 2.5 mm long, sub-erect to horizontal, cylindric and with a distinct neck, 

 arcuate to nearly symmetric, when dry and empty sometimes striate; lid conic, 

 obtusely acuminate to long-acuminate, about one-third as long as the urn; 

 annulus usually 2-seriate, large, revoluble; exothecial cells rounded-quadrate, 

 small at rim, gradually larger and more oblong below, all incrassate; peristome- 

 teeth lance-.subulate, hyaline and papillose above, yellowish and dorsally cross- 

 striolate below, strongly lamellate and trabeculate, confluent at base; segments 

 slender, as long as the teeth, basal membrane one-third as high, cilia 2 or 3, 

 usually 3, slender, nodose; spore3 smooth, medium-walled, yellowish, .008-011 

 mm, mature in summer. 



On stones, humus, and rotten wood, in moist forests; cosmopolitan in tem- 

 perate and cooler regions; in North America from the Arctic regions to the 

 northern United States and southwards in the mountains to Georgia. 



