American Paleozoic Bryozoa. 163 
such as characterizes these structures in other forms. The cell-walls 
are moderately thin, and as a rule hexagonal, though five and seven 
sided tubes are not uncommon. 
This species is distinguished externally from L. ornata, by its larger 
and more regularly arranged cells. Internally we find a greater 
number of diaphragms in the tubes of the former, than in those of the 
latter species. 
In many respects Z. cortex is closely related to such species of 
' Monotrypa, as UY. petasiformis, Nicholson, and M. filiasa, D’Orbigny. 
I am, however, slowly becoming convinced that those species do not 
really belong to the genus Monotrypa. They differ from Mf. undulata, 
Nicholson, the type of that genus, in several important features. In 
M. petasiformis, for instance, the tubes of the zoarium are divided 
into two distinct regions, equivalent to the axial and peripheral 
regions of the ramose Monticuliporide, The tubes in the axial or 
lower portion of the zoarium have very thin walls, and are crossed by 
remote diaphragms, which further up in the peripheral region become 
numerous and often crowded, while at the same time the walls are 
appreciably thickened, and show a distinct line of demarcation separat- 
ing adjoining tubes. Thestructure of MW. undulata is quite different, its 
zoarium being, in a measure, homogeneous throughout, and incapable 
of being divided into similarly differentiated regions. In this connec- 
tion it is important to note that a number of more or less distinct 
forms, differing, however, in no essential features from MM. undulata, 
oceur in Upper Silurian, Devonian, Lower Carboniferous, and Coal 
measure deposits, a fact going to show, that, though simple in structure, 
the genus Monotrypa is characterized by peculiarities distinct enough 
to be preserved throughout all the great divisions of the Paleozoic rocks, 
an extent of range enjoyed by but few of the genera of the Monticu- 
liporide. What to do with M. petasiformis and M. filiasa, I am not 
yet prepared to say, being unwilling to admit them into the genus Lepto- 
trypa. Their structure being very similar to the most typical species 
of Monotrypella, it might be well to extend the limits of that genus so 
that they would be included. 
Formation and locality: Cincinnati group. Specimens of Z. cortex, 
are rather rare in the lower 200 feet of strata exposed at Covington, 
Ky., and Cincinnati, O. 
DiscorryPa, n. gen. 
Gen. char. anée vol. v., p. 155. 
The type of this genus, and its only known representative was 
