CORALS AND BRYOZOA. 165 



other associated species of this geological formation, it differs in having angular, 

 sinuous branches, and in the size of the branches and fenestrules. 



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



Fenestella (Polypoka) hexagonalis, var. foraminulosa. 



PLATE XXXIX, FIGS. 16-20. 



FenesteUa hexagonalis, var. foraminulosa. Hall. Trans. Albany Institute, vol. x, abstract, p. 27. 1881. 

 " (Pulypora) hexagonalis, var. foraminulosa. Hall. Report of State Geologist for 1882. Expl. 



pi. 32. fig-s. I(i-20, 1883. 



This variety is very similar to the ordinary forms of F. (P.) hexagonalis, but 

 on the celluliferous face it has numerous, very prominent, hollow, conical nodes. 

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



Fenestella (Polypora) nexa. 



PLATE XXXIX, FIGS. 4-8. 



FenesteUa nexa. Hall. Trans. Albany Institute, vol. x, abstract, p. 25. 1881. 



" (Polypora) nexa. Hall. Report of State Geologist for 1882. Expl. pi. 32, figs. 4-9. 1883. 



Bkyozoum infundibuliform. Branches moderately strong, very gradually in- 

 creasing in size, width above a bifurcation .33 mm., increasing to .65 mm., 

 angular, slightly carinated, very seldom sinuous. Interstices usually a little 

 wider than the branches. Dissepiments comparatively slender, width .33 

 mm., angular, slightly carinated, on a plane with the branches, about three 

 in the space of 5 mm. Fenestrules oval, length about 1.20 mm., width 

 .50 mm. 



On the celluliferous face the branches are rounded. Dissepiments angular, 

 slightly carinated, much depressed. Fenestrules narrower than on the 

 opposite face, the interstices being slightly narrower than the branches. 

 Cell apertures in from two to four ranges, sixteen in the space of 5 mm., 

 separated by about the diameter of an aperture ; where only two ranges of 

 apertures occur, they are separated by a slightly elevated carina. 



This species may be distinguished from F. (P.) separata by the somewhat more 

 lax appearance of the frond, the more slender and less frequent branches and 

 dissepiments. 



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



