OF WESTERN PENNSYLVAXIA 133 



apiculate; calyptra long and erect-rostrate, mitrate, lobed to 

 the base of the beak, covering one-half or less of the capsule. 



A cosmopolitan genus of about 75 species ; 17 species in 

 North America, at least 2 species in our range. 

 Key to the Species. 



a. Seta very short; capsule immersed, wide-mouthed; calyptra small. 



1. P. iiiuiiersttin. 



a. Seta longer; capsule exserted, not wide-mouthed; calyptra larger. 



2. P turbinatum. 



1. Physcomitrium irnmersum Sullivant. 

 {Gymnostomum irnmcrsnui Sullivant). 

 (Plate XVI) 

 Plants small, erect, gregarious, light green, simple or 

 branching, 3-8 mm. high; leaves 1,5-3.5 mm. long, obovate 

 to oblanceolate, serrate above the middle, spreading to ascend- 

 ing; costa strong, ending a little below the apex; leaf-cells 

 parenchymatous, rather large and thin-walled, the basal rec- 

 tangular, about 2-5:1, the upper irregularly oblong, the 

 marginal narrower and in the alar region a few much shorter : 

 capsule immersed, globose to pyriform-globose, 0.6-0.9 mm. 

 in diameter, apiculate-rostrate, about the upper two-fifths con- 

 stituting the operculum, yellow-brown when ripe : seta con- 

 siderably shorter than capsule and stout ; exothecial cells ir- 

 regularly quadrate to hexagonal, somewhat incrassate, the 

 annulus consisting of one to three rows of much smaller, 

 orange-pellucid, to brown-pellucid cells, the cells of the wall 

 usually laterally elongated for one or two rows abo\'e and be- 

 low the annulus ; calyptra mitrate, the basal margin 4-3- 

 lobed, covering about one-half of the operculum ; spores dense- 

 ly papillose, orange to brownish-pellucid, globose, in our speci- 

 mens about .035 mm. in diameter, mature in autumn. 



Usually on clayey or sandy flood-plains where submerged 

 in time of freshets. Quebec to Colorado and Delaware but 

 not commonly collected, probably on account of its small size 

 and special habitat. 



Beaver : Clay bank of Little Beaver Creek, New 



Galilee, September 10, 1906. O. E. J.; 

 b.ank of Ohio River, Smith's Ferry, Oc- 

 tober 1, 1910. O. E. J. (Figured).' 

 AIcKean : East Branch, Bradford, June 13, 1895. D. 



A. B. 



2. Physcomitrium turbinatum (Richardson) C. Mueller. 

 (Phascuiii strangulatuiii Kindberg; Phascniii hookcri !Macoun). 



(Plate XVI) 

 Gregarious, often densely so, light green : stems 3-5 mm. 

 high, erect, usually simple; leaves i-S mm. long, lance-ob- 



