American Paleozoic Bryozoa. 165 
presents a variable number of slightly convex and irregularly angular 
spaces with an average diameter of about .15. At the margin of these 
convex spaces the cell-apertures are circular, and =4,th of an inch in 
diameter. The cell-apertures gradually become broadly elliptical, and 
larger as the centers of the spaces are approached, where the largest 
have a diameter of 4th inch. The apertures of the cells are often closed 
by a centrally perforated, thin operculum. The interstitial spaces are 
occupied by the elongated apertures of very shallow interstitial cells. 
The spiniform tubuli are quite numerous and prominent. 
In longitudinal sections (Pl. VIL, fig. 2c) the proper tubes are pros- 
trate for half their length, when they bend upward and proceed directly 
to the surface. Their walls are thin and more or less flexuous, 
especially upon the concave side of the tube. The interstitial tubes 
are developed from the upper wall of the prostrate portion of the proper 
zocecia, and enlarge very rapidly, so as to attain their full size, at the 
second diaphragm. In the proper tubes the diaphrams are present only 
in the lower half of the tube, where it is crossed by two or three. At 
their apertures a very thin calcareous line representing the opercula 
mentioned may sometimes be detected. In the interstitial tubes the 
diaphragms are crowded. ‘The spiniform tubuli are first developed 
near the cell-apertures, where if carefully looked for, a variable number 
may be detected. <A second layer of cells is often found above the first. 
Tangential sections (Pl. VIL, fig. 20) show that the cells have very 
thin walls, those of adjacent tubes being entirely separated, or in con- 
tact only at limited points. Their diameter becomes greater as the 
center of the convex spaces or monticules is approached, while they at 
the same time vary their shape from sub-circular to oval or elliptical. 
The interstitial spaces are occupied by large, usually hour-glass-shaped 
interstitial cells, which are occasionally divided into halves by a very 
faint wall. Comparatively large spiniform tubuli are developed at all the 
points where the true cells come in contact. 
This species in growth somewhat resembles Prasopora (?) newberry?, 
Nicholson, and the closely allied P. calycula, James ( Diplotrypa caly- 
cuia, Nicholson). Both those, however, have a smooth, and evenly 
convex upper surface, while the under surface is only concentrically, 
and not radially striated. 
Formation and locality: Rare in the shales just above low water 
mark in the Ohio river at Cincinnati, O. My specimens were collected 
on the banks of the river Ohio, in the first ward of the city. 
