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 carinas 

 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 (Hemitbypa) biordo, n. sp. 



NOT FIOCRBD. 



Bevozoum 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. 

 Carinae very thin, width of summit about .12 mm. Scalae and pseudo-carinae 

 of the same width ; eighteen scalae in the space of 5 mm. Interstices sub- 

 quadrangular, nearly square or sub-circular. When the scalae alternate the 

 carinas 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. 



