124 PALEONTOLOGY 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. 



The 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 ; the 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 Helderberg group. Falls of the Ohio river. 



