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. ( U .) 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. 
Fenestella tenella, Hall. Report of State Geologist for 1885, 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 
