CORALS AND BRYOZOA. 
135 
ranges of apertures carinated; height of carina about .70 mm., very thin be¬ 
low, then expanding to a width of about .25 mm., connected by very thin 
scalae, the summits of which are about .18 mm. wide. These processes ex¬ 
tend inward nearly to the branch, at first obliquely toward the base, then 
abruptly bending, continue in the opposite direction, fourteen in the space of 
5 mm. Interstices narrow, oval. The summits of the carinse extend above 
the scalae. 
This species very closely resembles F. (U.) tegulata, but the non-celluliferous 
face is more irregular, the dissepiments wider and the fenestrules smaller: on 
the celluliferous face the scalae are thicker and less oblique ; the summits of the 
carinae are wider and more elevated above the scalae; those of F. ( U.) tegulata, 
being sharp and either very slightly, or not at all, elevated above the connect¬ 
ing scalae. 
Formation and locality. Upper Helderberg group, Falls of the Ohio river. 
Fenestella (Unitrypa) tegulata. 
PLATE LI, FIGS. 15-23. 
Fenestella (Hemitrypa) tegulata, Hall. Trans. Albany Institute, vol. x, abstract, p. 34. 1881. 
“ (Unitrypa) “ “ Report of State Geologist for 1885, advance sheets. Expl. pi. 51, 
tigs. 15-23. 1886. 
Unitrypa retrorsa, Ulrich. Cont. Am. Pal., vol. i, No. 1, pi. 1, figs. 7 a, b, c. 1886. 
Bryozoum infundibuliform. Branches slender, width above a bifurcation .25 
mm., increasing to from .30 to .40 mm., very gradually enlarging, increase in 
size hardly perceptible, sub-parallel, straight or sinuous, rarely zig-zag, 
angular, slightly carinated ; bifurcations distant. Interstices wider than the 
branches. Dissepiments slender, width about .25 mm., angular, carinated, 
on the same plane or elevated above the branches, sometimes continuing 
across the branch, connecting with adjacent dissepiments and forming 
irregular, transverse ridges, very rarely prominent enough to obscure the 
branches, six in the space of 5 mm. Fenestrules oval, length from .50 to 
.60 mm., width .25 or .30 mm. 
On the celluliferous face the dissepiments are rounded, much depressed. 
Fenestrules narrower than on the opposite face. Cell apertures in two 
