124 
PALAEONTOLOGY OF NEW YORK. 
branches except for a short distance. Branches slender, width .30 mm., in¬ 
creasing to .50 mm., angular, slightly carinated, decidedly zig-zag, anasto¬ 
mosing or connected by very short dissepiments. Transverse section of a 
branch sub-cuneiform, thickness .75 mm. The dissepiments or anastomosed 
portions are wider than the branches, and elevated above their plane, con¬ 
tinuing across them, coalescing with those of adjacent branches, forming 
irregular continuous ridges, which are the most prominent feature of the frond, 
obscuring the branches and giving to the non-celluliferous face a stelliform- 
reticulate appearance. Fenestrules variable in form and size, oval, circular, 
or sometimes rhomboidal. 
Tbe celluliferous face of the frond presents a rigid appearance, the branches 
are slightly sinuous, very gradually enlarging, sub-parallel. Dissepiments 
very short, width .60 mm., rounded, depressed, five in the space of 5 mm. 
Fenestrules regularly oval, small, length .40 mm., width about .25 mm. Cell 
apertures in two ranges, opening somewhat laterally, twenty-four in the space 
of 5 mm., separated by less than the diameter of an aperture. Surface be¬ 
tween ranges of apertures carinated; carina .40 mm. in height, thin below, 
then expanding, the summit flat, and having a width of .30 mm. 
The two faces of the frond are so unlike each other that seen separately they 
would easily be mistaken for different species. The non-celluliferous face of 
this species may be distinguished from that of F. semirotunda by its coarser 
appearance; tbe celluliferous faces have little resemblance. Both faces of the 
frond very nearly resemble F. bi-imbricata, but the structure is not so coarse in 
appearance, the dissepiments and branches are smaller: there are four dissepi¬ 
ments in the same space occupied by two in that species; the dissepiments of 
F .bi-imbricata having frequently a width of more than 1 mm. From other species 
of similar manner of growth it may be distinguished by its size. 
Formation and locality. Upper Ilelderberg group, Falls of the Ohio river. 
