(139) 
Sections of stem show at the surface a layer of thin-walled 
cells next to several rows of thickened cells and mostly a 
central strand of 4 or 5 small cells, sometimes not distinct, 
however. The costa is in section plano-convex. Plates of 
teeth finely cross-lined (745). 
HypNUM AMBLYPHYLLUM R. S. Williams sp. nov. 
Dioicous. Growing in water up to 3.5 dm. high, with 
mostly short, subpinnate branches hooked at apex. Cross 
sections of stem 5-sided with distinct angles, a poorly devel- 
oped central strand of 3 or 4 small cells and outer walls of 1 
or 2 rows of thickened cells. Leaves below more or less 
spreading, flexuous and twisted, toward the tops of the stems 
and branches falcate-secund with the tips often abruptly in- 
curved. Stem leaves about 2.25 mm. long, serrulate all 
round, distinctly long-decurrent, ovate-lanceolate with broad, 
obtuse point, not plicate, somewhat concave, especially 
toward apex. Costa extending 2 up, slightly convex on 
back. Alar cells often inflated nearly to costa and some 
small, nearly quadratic cells at margin just above the alar 
cells. Medium leaf-cells .005 or .oo6 mm. wide and mostly 
.035 to .o60 mm. long. Younger branch leaves narrowly 
lanceolate with very short costa. Perichaetial leaves not 
plicate, closely sheathing, but little larger or more pointed 
than stem leaves, entire, with faint costa extending up % or 
more. Setaupto6cm. long. Capsule 2.5 by 1 mm., with 
short upright collum, but much curved and nodding above. 
Lid acutely conical, its height less than basal diameter. No 
annulus. Peristome teeth broadly hyaline bordered above, 
outer plates finely punctate below. Basal membrane of en- 
dostome scarcely ; the teeth in height with solid segments and 
2 or 3 nodose cilia between. Transversely elongated cells 
about mouth of capsule in 3 or 4 rows, the cells below 
roundish to oblong. Stomata roundish to short oblong, up 
to .o40 mm. long. Minutely roughened spores up to .o16 
mm. (Plate 24.) 
This species is intermediate between exannulatum and 
pseudostramineum. From the first it differs in the short, 
broadly-pointed leaves, the angular stem with fewer thickened 
cells in the outer walls and leaf-cells not pitted. The 
second differs in being monoicous, with entire, not decurrent 
leaves and not angular stems. 
