American Paleozoic Bryozoa. 249 
than the ordinary, which may be raised into low, rounded monticules, 
or remain on a level with the surrounding plane of the surface. Cells 
regularly arranged in diagonally intersecting lines, about twelve in the 
space of .1 inch, separated by interspaces, usually of less width than 
the diameter of their orifices, which averages about ;4,th of an inch. 
When in a good state of preservation (Pl. XIL., fig. 3), the cell apertures 
are distinctly floriform, the wall at each of the indentations, being raised 
into a small spine, repesenting the surface extension of the spiniform 
tubuli. Interstitial cells numerous, but not readily recognized exter- 
nally, being shallow, and much obscured by the spiniform tubuli. 
Tangential sections (Pl. XII, figs. 3¢@ and 36) show the characters 
of the genus and species in an excellent manner. The cell walls are 
very thin, and those of the true zoccia are more or less strongly 
indented at from two to five points in their circumference; the inden- 
tations are made most distinct by the spiniform tubuli, one of which 
occurs at each point, where it is developed, in nearly all cases, almost 
entirely upon the inner side of the wall. Surrounding, and usually 
completely isolating, the true cells, is a single, rarely double, row of 
small angular interstitial cells, with thin and rather faintly marked 
divisional walls. They are generally about half the size of the proper 
zocecia, and where three or four of them join, a spiniform tubulum ap- 
pears always to have been developed, but I have never detected these 
structures in their walls between the angles. Lastly, the majority of 
the proper zocecia show the cut edges of the cystoid diaphragms. 
Vertical sections, when cut from one of the typical incrusting ex- 
amples, are identical with what may be called the peripheral portion of 
the section represented by figure 3c, on Plate XII. All the tubes 
have equally thin walls, but the two kinds are readily distinguished 
from each other by their relative size and tabulation. In the intersti- 
tial tubes, which first come into existence a short distance above the 
attached epithecal base, the diaphragms are crowded, and always hori- 
zontal. In thelarger true zoccia! tubes, a series of rather large cystoid 
diaphragms is usually present along the concave wall; while, as is nearly 
always the case in forms of this character, the space intervening be-- 
tween the inner margin of this series and the opposite wall, is crossed 
by equally numerous straight diaphragms. The intervals between 
the diaphragms of the smaller tubes are about half as long as those 
separating these partitions in the larger tubes. 
Figure 3d represents a specimen in which the free condition of the 
zoarium is more distinct than in any other seen. However, in the ex- 
