156 
PALAEONTOLOGY OF NEW YORK . 
Fenestella (Polypora) robusta. 
PLATE XXXIV, FIGS 4-7 ; PLATE XXXVII, FIG. 1; PLATE XXXIX, FIGS. 1-3 ; AND PLATE XLVI, FIG. 6. 
Fenestella robusta. Hall. Trans. Albany Institute, vol. x, abstract, p. 22. 1S81. 
“ ( Polypora ) robusta. Report of State Geologist for 1S82. Expl. pi. 27, figs. 4-7 ; pi. 30, fig. 1 ; 
pi. 32, figs. 1-3. 1S83. 
Bryozoum infimdibuliform. Branches very strong, angular, sometimes with a 
slight carina; width just above a bifurcation .66 mm., increasing to 1.50 mm; 
bifurcations usually occur at intervals of from 20 to 50 mm. Interstices 
slightly wider than the branches. Dissepiments .66 mm. wide, four or five 
in the space of 5 mm., on the same plane with the branches and expanding 
at their junction. Fenestrules broadly oval. 
On the celluliferous face the branches are rounded. Dissepiments rounded 
or sub-angular, much depressed. Fenestrules elongate-oval, narrower than 
on the opposite face. Cell apertures in from four to seven ranges, eighteen 
in the space of 5 mm., separated longitudinally by slightly less than the 
diameter of an aperture; transversely they are nearly or quite in contact; 
margins strong, equally elevated. 
This is a characteristic species and will be easily distinguished from the 
associated forms, by the large size and rigid appearance of the branches. 
Formation and locality. Upper Helderberg group, Walpole, Ontario, Canada. 
Fenestella (Polypora) largissima. 
PLATE XXXIV, FIGS. 8, 9. 
Fenestella largissima. Hall. Trans. Albany Institute, vol. x, abstract, p 22. 18S1. 
“ (Polypora) largissima, Hall. Report of State Geologist for 1882. Exp], pi. 27, fig-s. 8, 9. 1883. 
Bryozoum infundibuliform, of coarse and irregular growth. Branches strong, 
angular, width above a bifurcation .90 mm., increasing to 1.50 or 2 min.; 
bifurcations at intervals of from 6 to 10 mm. Dissepiments strong, width 
about I mm. Fenestrules sub-quadrangular or oval, variable in appearance, 
length from 2 to 4 mm., width from 1 to 1.50 mm. Cell apertures in four to 
six ranges. 
This species may be distinguished by the large size of the branches and 
dissepiments and its irregular growth. 
