242 . PALEONTOLOGY OF NEW YORK. 



parallel with, or obliquely to the surface. Intercellular space occupied by 

 irregularly disposed vesicles. Cell apertures varying from elongate-oval to 

 nearly circular, disposed in longitudinal, divergent lines, increasing by 

 interstitial additions; apertures of marginal rows larger than the others. 

 Peristomes strong, equally or unequally elevated. Ranges of apertures sepa- 

 rated by more or less prominent ridges, which often continue obliquely 

 across the non-celluliferous space, and with the adjacent margins extend be- 

 yond the other portions, giving to the border a sinuate appearance. 



The variations of this species are so great that where only the extremes are 

 observed, they would naturally be regarded as belonging to different species. 

 On some fronds the cell apertures are circular, diameter about .18 mm., separated 

 by more than twice the diameter of an aperture ; on others they are oval, 

 length .35 mm., width a little more than one-half the length, margins in con- 

 tact: all intermediate forms occur. On some fronds the ranges of apertures 

 are separated by slender, slightly elevated striations, on others by broad flat- 

 tened ridges, wider than the apertures and obscuring them, on still others by 

 two or more striations, frequently one of the striations passing obliquely 

 between two apertures, and uniting with adjacent striations ; on most of the 

 fronds these markings are narrow, rounded and prominent. Upon those fronds 

 originally described as S. obliqua (pi. Ix, fig. 3), the ridges are slightly elevated 

 or frequently obsolete, the posterior portion of the peristomes is much the more 

 prominent, the apertures being very oblique and seemingly irregularly disposed, 

 varying gre.atly in appearance from the forms represented by figs. 7-13 of pi. Ix. 

 The forms described as S. muUipora are very narrow, having a width of only 2 

 mm., the apertures are minute, circular, diameter .15 mm., very closely dis- 

 posed, sixteen apertures in the space of 5 mm., being twice the number that 

 occur in the same space on some other forms of the species. Peristomes some- 

 times smooth, at other times denticulated ; on some fronds the denticulations 

 are invariably situated within the exterior margin of the aperture, are very slen- 

 der, not elevated above the peristome, frequently continuing nearly across the 

 opening, and in the course of growth forming two parallel ridges along the 

 inner face of the cell walls (pi. Ix, figs, 13, 14); on other fronds the denticula- 



