268 
PALAEONTOLOGY OF NEW YORK. 
varying from 10 to 15 mm., width near the base about 1.50 mm., very 
gradually enlarging to 3.50 mm.; on some fronds the branch is flattened 
immediately above the truncated base and the surface has the same appear¬ 
ance as above; on others the lower portion is cylindrical and striated, grad¬ 
ually becoming flattened ; the striae on different branches vary in appearance ; 
on one branch the striations continuing for the space of 8 mm., about fifteen 
in the space of 5 mm. measured transversely, a few of the striae being much 
stronger than the others; the contiguous branch has the lower portion for 
the space of 5 mm., striated, but a portion of the striae become compara¬ 
tively strong rounded ridges, seven ridges in the width of the branch; 
another branch has the rounded, finely striated ridges similar to the preced¬ 
ing, but between them are cell apertures which continue to the truncate 
base; these variations occur on the same frond. Non-celluliferous marginal 
space extremely narrow: transverse sections of a branch, for the greater 
portion of its length, are lenticular, obtusely angular at the middle, greatest 
thickness observed about .65 mm ; branches diverge at an angle of from 
thirty to forty-five degrees. Cells tubular, recumbent for a portion of their 
length, then abruptly curving and opening directly outward, gradually 
enlarging to the aperture. Intercellular tissue vesiculose, vesicles irregu¬ 
larly disposed. Cell apertures oval, width usually a little more than one- 
half the length, arranged in nearly parallel longitudinal rows, from eight 
to twelve rows on each face of the branch; the apertures of the marginal 
rows are slightly larger and more distant than the others, .33 mm. in length, 
eight or nine in the space of 5 mm.; on the central ranges the length is 
.25 mm., and there are fifteen in the same space. Peristomes very slight, 
posterior portion with a prominent projection, the extremities of which form 
two denticulations; the peristomes are often indistinct, and the denticulations 
are so extended as to give the appearance of minute, circular cell apertures 
or of a succession of loops. Ranges of apertures separated by continuous 
ridges, sometimes narrow, angular, and smooth, at other times broader, more 
prominent and finely striated, the central ridge is always the strongest and 
has the appearance of a carina. 
