164 PALEONTOLOGY OF NEW YORK. 



slightly wider than the branches. Fenestrules oval, length usually about 

 1.50 mm., width two-thirds the length. 



On the celluliferous face the branches are rounded, sinuous, never zig-zag. 

 The anastomosed portion is depressed below the center of the branches. 

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

 to five ranges, sixteen in the space of 5 mm., separated by less than half 

 the diameter of an aperture ; margins strongly elevated. 



This species most closely resembles F. hexagonalis, but may be distinguished 

 by its coarser growth ; from F. robusta, it may be distinguished by the zig-zag, 

 anastomosing branches on the non-celluliferous face. 



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



Fenestella (Polypora) hexagonalis. 



PLATE XXXVin, FIGS. 14-20. 



Fenestella hexagonalis. Hall. Trans. Albany Institute, vol. x, abstract, p. 27. 1881. 



(Polypora) hexagmMlis,\iku.. Report of State Geologist fori 8S2. Expl. pi. 31, figs. 14-20. 1883. 



Bryozodm infundibuliform, fronds large. Branches strong, very gradually en- 

 larging, width above a bifurcation .50 mm., increasing to .75 mm., angular, 

 with a slight carination, usually sinuous, sometimes anastomosing ; bifurca- 

 tions usually occur at intervals of from 20 to 50 mm. Interstices slightly 

 wider than the branches. Dissepiments strong, width from .50 to .70 mm., 

 three in the space of 5 mm., angular, carinated, on a plane with the 

 branches. Fenestrules oval, length usually about 1 mm., width .60 mm. 



On the celluliferous face the branches are rounded and sinuous. Dissepi- 

 ments rounded, depressed. Fenestrules narrower than on the opposite face, 

 width about .40 mm. Cell apertures in from two to four ranges, sixteen in 

 the space of 5 mm., closely disposed, frequently in contact; margins distinctly 

 elevated. The central range is often very prominent. 



This species may be distinguished from F. {P.) perundaia, by the smaller and 

 more regular branches, which are usually connected by dissepiments ;. from the 



