170 PALEONTOLOGY OF NEW YORK. 



trules narrower than on the opposite face. Cell apertures in from three to 

 six ranges, usually either four or six ranges, opening outward and laterally ; 

 twelve in the space of 5 ram., separated by less than half the diameter of an 

 aperture : margins equally elevated. There is usually a prominent, rounded 

 ridge along the middle of the branch, which is smooth or nodose. 



This species may be distinguished from nearly all others of this geological 

 formation, by the size of the branches, dissepiments and fenestrules ; it is the 

 only form of Polypora, at present known, having a prominent, nodose ridge 

 along the middle of the branch. The only species to which it has a close re- 

 semblance is F. (P.) largissima, but the branches are a somewhat more slender, 

 the bifurcations more distant, the fenestrules narrower and the whole frond, 

 though irregular, is much more regular than in that species. 



Formation and locality. Upper Helderberg group, Walpole, Ontario, Canada. 



Fenestella (Polypora) crebescens. 



PLATE XLV, FIGS. 20, 21. 



FinesteUa crebescens. Hall. Report of State Geologist for 1885, advance sheets. Expl. pi. 45, figs. 20, 



21. 1886. 



Bryozoum infundibuliform. Branches moderately strong, width above a bifur- 

 cation .35 mm., increasing to .65 mm., rounded, rigid, with prominent nodes, 

 which are irregularly disposed and frequently occurring opposite a dissepi- 

 ment. Interstices narrower than the branches. Dissepiments strong, width 

 .35 ram., rounded, slightly depressed, eleven in the space of 5 mm. Fenes- 

 trules oval, length about .55 mra., width frora one-half to two-thirds the 

 length. 



Celluliferous face not observed. 



This species is referred to the genus Polypora on account of the compara- 

 tively great width of the branches, which indicate the existence of more than 

 two ranges of cellules. 



Formation arid locality. Upper Helderberg group. Western New York. 



