CORALS AND BRYOZOA. 105 



On the celluliferous face the dissepiments are rounded and depressed. 

 Fenestrules much narrower than on the opposite face. Cell apertures in 

 two ranges, opening directly outward ; thirty in the space of 5 mm. ; very 

 closely disposed, frequently in contact : margins distinctly elevated, indenting 

 the borders of the fenestrules ; often immediately below a bifurcation, and 

 sometimes on other portions of the branch, there are large cell apertures 

 having twice the diameter of the ordinary apertures. Branches between the 

 ranges of apertures angular, with a line of nodes along the middle. 



This species, on the non-celluliferous face, presents so variable an appearance 

 that different fragments might be considered as belonging to different species. 

 Where the frond is macerated the elevated margins of the cell apertures are 

 obsolete, and the apertures apparently open laterally. The nodes are also 

 obsolete. The non-celluliferous face cannot be distinguished from that of 

 F. (f/.) acaulis. It very closely resembles F. serrata, but the frond is more 

 compact, the fenestrules much smaller, the branches of the celluliferous face 

 less angular. The branches and dissepiments are smaller and more closely 

 arranged than those of F. stellata. 



Formation and locality. Upper Helderberg group. Falls of the Ohio river. 



Fenestella tenella. 



plate xlv, figs. 18, 19. 



Feneitdla tenella, Ha.ll. Report of State Oeologist for ISSS, advance sheets. Expl. pi. 45, figs. 18, 19. 1886. 



Bryozoum infundibuliform, compact. Branches very slender, width just above 

 a bifurcation .18 mm., increasing to .35 mm., rigid, angular, with small 

 irregularly disposed nodes. Interstices of the same width as the branches. 

 Dissepiments extremely slender, width about .18 mm., rounded, slightly 

 depressed, eight or nine in the space of 5 mm. Fenestrules oval, length 

 from .35 to .40 mm., width from one-third to one-half the length. 



On the celluliferous face the dissepiments are rounded and depressed. 

 Fenestrules as on the opposite face. Cell apertures in two ranges, opening 

 outward ; twenty-eight in the space of 5 mm., separated by less than the 



