128 _LEJEUNEAE OF THE UNITED STATES AND CANADA 
species, but intermediate thickenings in A. xanthocarpa are very | 
infrequent. 
3. Archilejeunea conchifolia sp. nov. 
PLATE 17, FIGS. 1-9 
Pale yellowish-green or whitish, growing in depressed mats: _ 
stems prostrate, 0.1 mm. in diameter, closely appressed to matrix, 
irregularly branched: rhizoids abundant: leaves densely imbri- 
cated, the lobe obliquely spreading, not falcate, ovate, very con- 
vex, 0.7 mm, long, 0.45 mm. wide, strongly revolute at the 
rounded apex and along the postical margin, antical margin slightly 
rounded at base, arching across or just beyond axis, margin entire 
or very vaguely and sparingly crenulate ; lobule inflated, oblong, 
0.45 mm. long, 0.17 mm. wide, keel more or less arched, usually 
forming a continuous line with the revolute postical margin but 
sometimes slightly indented at junction with postical margin, free 
margin curved, involute to or beyond apex, sinus beyond apex 
deep and rounded then passing very obliquely into the revolute 
postical margin, apex acuminate, the apical tooth mostly three to 
six cells long and three or four cells wide at base, ending in a 
single row of two or three cells; cells of lobe slightly papillose, 
with thickened free walls and thin vertical walls, trigones small, 
intermediate thickenings very scanty near base of lobe, otherwise 
wanting, cells at edge of lobe 14 A in diameter, in the middle and 
at the base 20 p: underleaves contiguous or imbricated, broadly 
obliquely or widely spreading, rounded at the apex, 7 
mm. long, 0.45 mm. wide, lobule narrowly ovate to lingulate, ob- 
tuse to acute at the apex, 0.45 mm. long, 0.17 mm. wide ; bracteole _ 
obovate, 0.5 mm. long, 0.35 mm. wide, narrowed toward base, 
eels sharp, antical keel distinct, about half as long as perianth, 
postical keel long, broad and sharply two-angled when young, 
keels smooth or nearly so: 4 spikes occupying short branches, | 
similar to those of 4. clypeata. 
Type-locality, Orange Bend, Florida (Underwood, 60). 
