American Paleozoic Bryozoa. 257 
section, show, that with only a few exceptions, all of the true zoccia 
have the concave wall lined with a more or less complete series of them. 
By comparing his tangential section, represented by fig. 40, with fig. 
4c, I think it will be seen at a glance that they have nothing in com- 
mon. Aside from the absence of cystoid diaphragms in fig. 4c, they 
differ so widely in the thickness of their intertubular spaces, that I am 
surprised at its being overlooked by so acute an observer as Dr. 
Nicholson has often shown himself to be. My vertical sections further 
show (FI. XII, fig. 7a), that the zoarium often consists of two layers, 
each with a maximum thickness of .02 of an inch or less. In some 
parts of a section, especially where it passes through one of the monti- 
cules, the spiniform tubuli, and the horizontal diaphragms in the in- 
terstitial tubes, have a peculiar intermittent, almost beaded appearance. 
Such an appearance is also exhibited by other Monticuliporide, but 
I can not, as yet, offer an explanation. Besides the cystoid diaphragms, 
one or two straight ones are usually present in eacb of the true cells. 
Formation and locality: Cincinnati group. This is the only com- 
paratively common representative of the genus. It is restricted to the 
beds marking the tops of the hills about Cincinnati, and seems to 
occur at all localities where those or equivalent strata are exposed. 
TREMATOPORA, Hall, 1852. 
This genus, as it was originally defined in the Pal. N. Y., Vol. IL., 
p. 149, and as Prof. Hall and other authors still use it, is un unwieldy 
and heterogeneous assemblage of forms, comprising, at the present day, 
representatives’ of no less than four distinct genera. ‘The author not 
haying designated a particular species as the type of the genus, I will 
regard the first species following the generic diagnosis, as the typical 
one. This course is the one usually adhered to, and, in my opinion, 
is the only justifiable one in such cases. Having made three series of 
sections from authentic specimens of Trematopora tuberculosa, Hall, 
I think I am prepared to furnish a clear definition of the genus as 
typified by that species. 
TrematTopora, Hall (Emend. Ulrich). 
Zoaria ramose, branches solid, sometimes tuberculated, generally 
smooth. Cells of two kinds, the true zocecia marked by oval or sub- 
circular apertures, and a more or less elevated peristome. The inter- 
stitial cells are numerous, sometimes completely isolating the true 
cells ; in the best preserved mature examples, their apertures, the out- 
