82 Cincinnati Society of Natural History. 
AMERICAN PALAOZOIC BRYOZOA. 
By E. O. Uxricsz. 
[Continued from Vol. 5, p. 257. | 
AMPLEXOPORA RoBUSTA, n. sp. (PI. L, figs. 1, la, 10.) 
Zoarium ramose, consisting of cylindrical, oftener of flattened 
branches, dividing dichotomously at rather frequent but irregular in- 
tervals, and usually varying in diameter from .4 inch to .7 inch. A 
very large specimen in my cabinet has a length of 4.3 inches; the cen- 
tral stem is flattened, and varies in diameter from 1.1 inches to 1.7 
inches. The bases of two branches are on one side, and three on 
the other, the mean diameter of which is about .6 inch. Monticules 
are not developed. The cells are moderately thin-walled, polygonal, 
and consist of one kind only (7.e., the interstitial cells are wanting); 
their arrangement is quite regular, and, when well preserved, show at 
their angles of junction the elevated points of the spiniform tubuli 
(Pl. I, fig. 1). At intervals of about .15 inch the surface exhibits con- 
spicuous clusters of cells larger than the average, with a mean diame- 
ter of {jth of an inch. The smaller or ordinary cells have a diameter 
varying from ;4,th to th of an inch. 
Tangential sections (PI. I., fig. la) show that the cell-walls are com- 
paratively thin and polygonal, and that their cavities are only occa- 
sionally rounded by a secondary deposit of sclerenchyma; and further 
that the original line of separation between adjoining cells is always: 
more or less distinctly marked. The spiniform tubuli do not consti- 
tute a conspicuous feature in sections of this species, and unless care- 
fully examined might be overlooked. With an occasional exception 
they always occupy the angles of junction of the cells. (Their appear- 
ance is very well represented by the figure.) Lastly, in many sections 
some of the cell-cavities inclose a small circular ring, that is due to 
the peculiar funnel-shaped diaphragms seen in longitudinal sections. 
In longitudinal sections (PI. I., fig. 16) the tubes in the “immature” 
region are thin-walled, and crossed by straight diaphragms from two 
to four tube-diameters apart. The nearly equal curve of the tubes, 
from the axis of the branch to the peripheral portion, constitutes a 
characteristic feature of the species. As they enter the peripheral or 
“mature” region their walls are considerably thickened, and the dia- 
phragms become much more numerous, being from less than one half to 
