244 PALEONTOLOGY OF NEW YORK. 



directly outward. Intercellular space occupied by irregularly disposed 

 vesicles. Cell apertures oval, length about .18 mm., width two-thirds the 

 length, disposed in regular longitudinal rows, about eight rows on each 

 face of the branch ; apertures of the marginal rows slightly larger than 

 the others, and are sometimes indistinctly trilobate in form. Peristomes 

 thin, distinctly and equally elevated, usually smooth, but sometimes with 

 indications of slight denticulations on the posterior wall. The non-celluli- 

 ferous Hiargin and interapertural space are marked by thin sharp striations, 

 which are elevated equally with the peristomes ; from two to four striations 

 between iidjacent ranges of apertures, often presenting an irregular appe.ar- 

 ance : the lower portion of the frond, for the space of 10 mm. or more, is 

 very frequently entirely covered by the striations, and sometimes nearly the 

 entire frond is similarly marked, the cell apertures sometimes faintly show- 

 ing beneath, but very often they are obsolete or covered. 



This species may be distinguished from S. indsurata by the more nearly par- 

 allel m.argins and ranges of apertures, the finer and more numerous longitudinal 

 striations, the narrower and finely striated non-celluliferous margin which is 

 entire, never notched or serrated. It most- nearly resembles S. tumulosa, 

 but may be distinguished by the larger, more oval cell apertures, which never, 

 so far as observed, h.ave a pustuliforra appearance, and by the more numerous 

 longitudinal striations over the greater portion of the frond : from S. incras- 

 sata, by its more slender form, smaller cell apertures, narrower non-celluliferous 

 margin, and the numerous longitudinal striations : from S. rigida, of the Upper 

 Helderberg group, by the less rigid appearance of the frond, the flat inter- 

 apertural space, and the finer, more numerous striae: from S. crescens, by the 

 presence of fine striations in place of prominent ridges : from S. interstriata, by 

 the coarser and continuous longitudinal ridges : from the other species, at 

 present known, from the Lower and Upper Helderberg and Hamilton groups, 

 it may be distinguished by the flat interapertural space, and the fine, some- 

 what irregular longitudinal ridges. 



Formation and localities. In the shales of the Hamilton group, Moscow, Liv- 

 ingston county, and near Canandaigua Lake, N. Y. 



