106 PALEONTOLOGY OF NEW YORK. 



diameter of an aperture. Surface carinated ; carinas slightly elevated, 

 strong, nodose ; nodes small, regularly disposed. 



This species may be distinguished from F. depressa by the smaller size of the 

 branches ; from F. tenuis by its larger branches, and from F. serrata and allied 

 forms by its more delicate appearance. 



Formalion and locality. Upper Helderberg group. Falls of the Ohio river. 



Fenestella pertenuis. 



PIJITE XLV, FIGS. 22, 28. 



Fhtetldla pertetiuis, Hall. Trans. Albany Institute, vol. x, abstract, p. 29. 1881. 



" " " Report of State Geologist for 1885, advance sheets. Expl. pi. 45, figs. 22, 23. 



1886. 



Bryozoum infundibuliform. Branches very slender, rigid, rounded, smooth, 

 width just above a bifurcation .15 mm., increasing to .25 mm. Interstices 

 as wide or wider than the branches. Dissepiments comparatively strong, 

 width .15 to .18 mm., rounded, on a plane with the branches, twelve in the 

 space of 5 mm. Fenestrules oval or sub-quadrangular, length from .25 to 

 .30 mm., width from .20 to .30 mm. 



On the celluliferous face the dissepiments are rounded, depressed. Fenes- 

 trules narrower than on opposite face. Cell apertures in two ranges, opening 

 outward ; thirty in the space of 5 mm. ; separated by less than the diameter 

 of an aperture : margins indenting the borders of the fenestrules. Branches 

 carinated ; carinae broad, slightly elevated, nodose ; nodes comparatively 

 large, regularly disposed, equal in number to the cell apertures. 



This species may be distinguished from F. tenella by the nearly equal size of 

 the branches and dissepiments ; the dissepiments being on a plane with the 

 branches. From nearly all other species it may be distinguished by the small 

 size and close arrangement of the branches and dissepiments. 



Formation and locality. Upper Helderberg group, Falls of the Ohio river. 



