264 PALEONTOLOGY OF NEW YORK. 



sharp elevation ; greatest thickness, without the elevation, from .50 to .75 

 mm. ; bifurcations on the specimens observed occur at intervals of from 15 

 to 30 mm. ; lateral briinches very frequent, occurring usually at intervals of 

 from 5 to 8 mm. ; lateral branching and bifurcation sometimes occur together 

 giving to the branch a trifurcating appearance ; the branches usually diverge 

 at an angle of about forty-five degrees. Cells tubular, cylindrical, gradually 

 enlarging to the apertures; in the triangular branches they proceed from 

 laminae which radiate from the center to each angle of the branch; 

 in the flattened branches they proceed from the mesotheca, and are 

 recumbent for about one-half their length, then abruptly turning and gener- 

 ally opening directly outward (pi. Ixii, fig. 18) ; at the center of the branch 

 their direction is parallel to the axis of the frond, each succeeding row of 

 cells becoming more and more divergent until frequently the marginal cells 

 are nearly rectangular to the axis (pi. Ixii, fig. 19). Intercellular tissue 

 vesiculose ; near the base the vesicles are large, smaller and more compactly 

 disposed near the surface. Cell apertures disposed in longitudinal paral- 

 lel rows, and very frequently in oblique ascending rows, from the middle of 

 the branch ; usually six or eight longitudinal rows on each face of the branch ; 

 the apertures of the central rows are minute, circular, with a diameter of 

 about .12 mm., sixteen in the space of 5 mm. ; marginal apertures sometimes 

 circular, diameter .25 mm., at other times oval, length .30 mm., width two- 

 thirds the length, ten in the space of 5 mm. ; sometimes the apertures, with 

 the exception of those of the marginal rows, are of the same size ; at other 

 times those of the central range are the smallest, those of each succeeding 

 range being a little larger; on some fronds the apertures are distinctly 

 papilliform. There is often a prominent, angular carina along the middle of the 

 flattened branch, which has a height of from .50 to .75 mm., and a width at 

 the base of .25 mm., generally straight, but sometimes a little sinuous; the 

 sides of the triangular branches are concave and have no ridges or carina. 

 Usually there are not more than eight ranges of apertures, and forms occur 

 having only four ranges, while others have ten, but as all intermediate 

 gradations occur, no specific distinction can be based upon this character; 

 there is also considerable variation in the strength of the carina. 



