CORALS AND BRYOZOA. 
155 
face. Cell apertures in two and three ranges, fifteen in the space of 5 mm., 
separated by the diameter of an aperture, central range the most prominent. 
When only two ranges occur they are separated by a slightly elevated 
carina. 
The general appearance of this species is similar to F. parallela , but the 
branches are larger, the dissepiments occur at less frequent intervals, and there 
are more than two ranges of cell apertures. From other forms it is distinguished 
by the distant bifurcations, and the straight, essentially parallel branches. 
Formation and locality. Upper Helderberg group, Walpole, Ontario, Canada. 
b. Forms having three or more ranges of cell apertures. 
Fenestella (Polypora) rigida. 
PLATE XXXIV, FIGS. 1-3. 
Fenestella rigida. Hall. Trans. Albany Institute, vol. x, abstract, p. 22. 1S81. 
“ ( Polypora) rigida, Hall. Report of State Geologist for 1882. Expl. pi. 27, figs. 1-3. 1883. 
Bryozoum infundibuliform. Branches moderately strong, angular, width above 
a bifurcation .50 mm., increasing to 1 mm.; bifurcations at intervals of 
from 10 to 20 mm. Interstices slightly narrower than the branches. Dis¬ 
sepiments slender, width .40 mm., four in the space of 5 mm., depressed 
below the plane of the branches and much expanded at their junction. 
Fenestrules broadly oval, width equal to two-thirds the length. 
On the celluliferous face the branches are rounded and the dissepiments 
depressed. Fenestrules of the same appearance as on the opposite face. 
Cell apertures in from three to five ranges, which are separated by a slightly 
elevated, sinuous ridge; sixteen apertures in the space of 5 mm. 
Formation and locality. Upper Helderberg group, near Thompson’s lake, 
Albany county, N. Y. 
