American Paleozoic Bryozoa. 155 
ters of cells slightly larger than the average. Between the individual 
cells composing these groups, there are always a greater or less num- 
ber of much smaller interstitial (7) cells, which are sometimes aggre- 
_ gated in sufficient numbers to constitute ‘‘macule.’’ Cells with mod- 
erately thin walls, those of the ordinary size about ~4,th of an inch in 
diameter, while that of those in the clusters mentioned does not exceed 
goth of an inch. 
In longitudinal sections the tube-walls are seen to differ but slightly 
in thickness in the axial and peripheral regions. Diaphragms are very 
sparingly developed, no tube, so far as I have been able to observe, 
being provided with more than two or three, throughout its length. 
The spiniform tubuli may be observed in large numbers, with the 
usual structure. None of the smaller tubes differ in their tabulation 
from the ordinary ones, and we may therefore assume, with some cer- 
tainty, that true interstitial tubes are absent. The bending of the 
tubes from the axial into the peripheral regions is quite uniform and 
gradual. 
Tangential sections show that the ordinary cells have thin walls, 
those of the slightly larger cells in the clusters described, being some- 
what thicker. The spiniform tubuli are somewhat variable in size, 
and very numerous for a species of Detayza, since nearly every angle 
of junction between the cells is occupied by one. A variable number 
of small cells is always present, These are, however, mostly de- 
veloped between the large cells of the clusters. What their nature is 
doubtful, but, as before intimated, it is highly probable that they are 
only young tubes. 
The large number of Spunifonin tubuli will serve to distinguish this 
species from all the other forms of the genus known to me. In its 
other characters the species is quite closely allied to D. aspera. 
Formation and locality: Cincinnati group. Rare at an elevation of 
about 425 feet above low water mark in the Ohio river, on the hills 
back of Cincinnati, O. 
PETIGOPORA GREGARIA, n. gen. et. sp. (PI. VII., figs. 3, 3a, 3b and 3c.) 
Gen. char. ante vol. v., p. 155. 
Zoarium consisting of small patches usually from .1 to .3 of an 
inch in diameter, and .04 inch in thickness, adhering to foreign 
bodies. Nearly all of my specimens are attached to Heterotrypa 
JSrondosa, D’Orl:. A narrow, usually smooth, but sometimes slightly 
wrinkled, germinating membrane forms the outer margin, which is 
