522 
usually in compact mats, branches obtuse, very rarely subatten- 
uate: dorsal lobes of leaves rather densely imbricate, appressed, 
or with the superior margin ascending or slightly reflexed, ob- 
liquely ovate to obliquely orbicular-ovate, rounded-obtuse, .85-2.1 
mm. x .65—-1.7 mm., apex more or less decurved, superior margin 
repand-dentate or subentire, the inferior sometimes a little undu- 
late-crisped, cells at inferior basal angle scarcely smaller, trigones 
distinct ; ventral lobes somewhat obliquely ovate to oblong, ob- 
tuse, rarely subacute, .4-I.2 mm. x .25—.85 mm., length about 
8 the width of the dorsal, nearly equaling underleaves in width 
or only one half as broad, margins, especially the outer, recurved, 
entire or with a single acute tooth at base, scarcely decurrent ; 
underleaves approximate or subimbricate, semiorbicular to quad- 
rate-oblong, rounded-obtuse, margins reflexed especially at apex, 
long-decurrent, sometimes repand or sparingly denticulate at base, 
otherwise entire: diocious: ¢ spikes oval to oblong, 1.2-3 mm. 
in length; 9 branch short; dorsal lobes of bracts obtuse, more 
rarely acute, the ventral lobes usually acute, margins of both en- 
tire or denticulate ; perianth oval, inflated ventrally along median 
line especially when young, narrowed above, the lips denticulate 
or subciliate, plane, or often lightly revolute, especially toward the 
_ lateral margins: capsule oval, light brown, the valves often irregu- 
larly split ; spores 32-45 y, echinulate, elaters 180-250 # x 7-10 #, 
2-(1-) spiral. 
Exsicc. Drumm. Musc. Am. (Southern States) 169. 
* Musc. Allegh. 263. 
Hep. Bor-Am. 89, 90, and 91 c (as Madotheca rivularis var. ?). 
Hep. Am. 29. 
Can. Hep. 9. 
On tree-trunks, logs, rocks, and soil. Very common in east- 
ern, northern, southern and central North America. Wyoming 
(Mayhew) ; Idaho (Leiberg, no. 8, 1888) ; Vancouver Island, 
near Victoria (Macoun, May 15, 1893, on young fir trees, no. 29); 
Ontario (Mrs. Roy, Macoun); Quebec (Faxon); Nova Scotia 
(ex. herb. James, collector unknown). 
Extremely variable. Most of the American specimens belong 
to Porella thuja, as defined by Lindberg, characterized by the 
somewhat regular pinnate branching, closely appressed obliquely _ 
rotund-ovate dorsal lobes, and oblong ventral lobes, the latter 
nearly or quite as broad as the underleaves. This appears to be 4 
