268 PALEONTOLOGY 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. 



