354 MUSCI. 



which overlap at the ends are parenchymatous. Their outer surface may be smooth or produced 

 into simple or forked papillse. These characteristics of leaf-structure are largely relied upon in 

 the definition of the tribes, as well as frequently of genera and species. The systematic arrange- 

 ment of the mosses is still to some extent unsettled. The limits of genera vary very much with 

 different authorities, and the principles which govern their disposition vaiy as widely. In the 

 following arrangement, while adopting essentially the method developed by Schimper most fully 

 in the second edition of his Synopsis Muscorum Europaeorum, his groupings are modified by a con- 

 solidation of some of the tribes, while less prominence is given to the numerous minor divisions 

 proposed by him. Under the last tribe Hi/pncce it has seemed advisable to deviate frequently 

 from his order. It has not been found always easy to express clearly and definitely the distinc- 

 tions which determine the several tribes and genera, but it is hoped that the key will in most 

 cases serve satisfactorily its intended purpose. The descriptions of the genera and species are 

 drawn almost wholly from published works, and are intended only as a temporary aid to the study 

 of the western species pending the publication of the more critical and authoritative Manual of 

 North American Mosses, by Messrs. Leo Lesquereux and Thomas P. James, which is now in 

 course of preparation. Acknowledgments are due to Mr. James for assistance in questionable 

 cases of synonymy, range, etc. 



I. Capsule without operculum, dehiscing irregularly. Fruit terminal on the main stem. 



TRIBE I. PHASCE^E. Minute terrestrial plants, stemless and bud-like or with a short mostly 

 simple stem. Capsule rarely exserted, globose to ovate-oblong. Flowers monoecious or 

 sometimes bisexual. 



* Prothallus filamentose, persistent : leaves coarsely serrate or incised, the areolation loose and 



uniform : columella none. 



1. Ephemerum. Very minute, annual. Calyptra campanulate. Capsule globose-ovate, api- 



culate, subsessile. 



* * Prothallus not persistent : leaves entire or nearly so, the areolation narrower toward the 



apex : columella present. 

 +- Leaves broadly lanceolate, crowded, more or less papillose. 



2. Sphaerangium. Acaulescent, bud-like, with deeply concave subscarious leaves. Capsule 



globose, not apiculate, immersed. Calyptra mitriform. 



3. Phascuni. Stouter, more caulescent. Leaves broadly lanceolate. Capsule subglobose to 



ovate-oblong, apiculate. Calyptra cucullate. 



-i- -f- Leaves narrowly lanceolate, the lower remote, not papillose, shining : stem at length 



branching below the summit. 



4. Pleuridium. Capsule ovate-globose, without collum, apiculate, shortly pedicellate. Calyp- 



tra cucullate. Male flowers axillary or hypogynous. . 



5. Bruchia. Capsule ovate-oblong, with large thick collum, rostellate, exserted. Calyptra 



mitriform. Male flowers terminal, bud-like. 



II. Capsule dehiscing by a deciduous operculum. Fruit terminal on the main stem or rarely 

 on short lateral branches. 



TRIBE II. POTTIES. Caulescent perennials (or annuals in Pottia), with the areolation 

 round-hexagonal above, mostly looser and hyaline and more rectangular at the base of the 

 leaves. Flowers bud-like. Calyptra cucullate (mitriform in a species of Pottia), long- 

 beaked. Capsule without collum, erect or nodding, on an exserted pedicel. Peristome 

 simple, of 16 teeth, entire or bifid or more or less completely divided, sometimes imperfectly 

 developed or wanting. 



* Leaves alternate, -in several ranks. 



+- Peristome none (except in a species of Pottia) : capsule subglobose to oblong : operculum 



obliquely rostrate or obtuse. 



6. Gymnostomum. Low perennials, on rocks. Leaves lanceolate or linear-lanceolate, of 



close firm texture, crenulate or subserrate. Capsule long-pedicellate, and conic opercu- 

 lum long-rostrate. 



7. Pottia. Very small terrestrial annuals or biennials. Leaves soft, oblong or oblong-obovate, 



rarely sen-ate. Capsule immersed or exserted, and the plano-convex or conic operculum 

 more or less rostrate or obtuse. 



+- -j- Peristome-teeth entire or bifid at the apex or unequally cleft to or below the middle : cap- 

 sule more or less oblong or cylindrical, long-pedicellate : leaves lanceolate. 



8. Weissia. Teeth entire or bifid at the apex only. Capsule oval or oblong, erect. Leaves 



entire, involute and crisped when dry. 



9. Dicranum. Teeth unequally cleft to the middle. Capsule nodding or erect, often incurved. 



Leaves frequently serrate toward the apex, often large. 



