CORALS AND BRYOZOA. 
149 
sembles that of F. (H.) cribrosa that it is very difficult to distinguish them, but the 
branches are angular, slightly carinated, never nodose as in that species. On 
the celluliferous face the difference is more apparent; the summits of the carinae 
and the scalae in this species are sharp, while in that species they are expanded 
and flat, the interstices are smaller and surrounded by a slight elevation, but 
the two forms are very nearly related. 
Formation and locality. Upper Helderberg group, Walpole, Ontario, Canada. 
Fenestella (Heriitrypa) biordo, n. sp. 
NOT FIGURED. 
Brvozoum infundibuliform, fronds large, compact. Branches slender, width 
above a bifurcation .25 mm., increasing to .50 mm., very gradually enlarging, 
increase in size scarcely perceptible, sub-parallel, rounded and smooth on the 
specimens observed; bifurcations distant. Interstices wider than the branches. 
Dissepiments comparatively strong, width .35 mm., rounded, sometimes 
slightly carinated, on a plane with the branches or elevated above, sometimes 
continuing across the branch, coalescing with adjacent dissepiments and 
forming very irregular, transverse ridges, which though prominent, do not 
obscure the branches, nine in the space of 10 mm. Fenestrules regularly 
oval, length .55 mm., width from .35 to .40 mm. 
On the celluliferous face the branches are straight and rigid. Dissepiments 
rounded, very much depressed. Fenestrules narrower than on the opposite 
face, the length being more than twice the width. Cell apertures in two 
ranges, opening laterally at an angle of about forty-five degrees, sixteen in 
the space of 5 mm., separated by less than the diameter of an aperture: 
margins slightly elevated, not indenting the borders of the fenestrules. 
Carinas very thin, width of summit about .12 mm. Scalae and pseudo-carinae 
of the same Avidth; eighteen scalae in the space of 5 mm. Interstices sub- 
quadrangular, nearly square or sub-circular. When the scalae alternate the 
carinae and pseudo-carinae are zig-zag, this surface of the frond then having 
the appearance of being composed of hexagonal cells, resembling the surface 
of a Favosites. 
