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, FIGa 1-3. 



Fenestdla rigida. Hall. Trans. Albany Institute, vol. x, abstract, p. 22. 1881. 



(Polypora) rigida. Hall. Report of State Geologist for 1882. Expl. pi. 27, ^gs. 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, sinuou.s ridge ; sixteen apertures in the space of 5 mm. 



Formation and locality. Upper Helderberg group, near Thompson's lake, 

 Albany county, N. Y, 



