American Paleozoic Bryozoa. 157 
and much more distinct than it is in any other species of the genus. 
From the latter the type species is further separated by its smooth 
often concave upper surface. 
Formation and locality : Cincinnati group. Rather rare on the hills 
back of Cincinnati, O., at an elevation of 425 feet above the river bed. 
The range is not positively known, but I found two groups of zoaria 
neariy 300 feet lower in the series. 
PETIGOPORA ASPERULA, n. sp. (PI. VI., figs. 4, 4a, 46 and 4c. ) 
Zoarium adhering to foreign objects, such as the shells of Stropho- 
mena alternata, etc., consisting of thin subcircular expansions, from 
.2 to .5 of an inch in diameter, and .03 to .08 of an inch in thickness. 
The surface is studded with small conical elevations, arranged in quite 
regular intersecting series, six or seven in the length of .4 of an inch. 
They are occupied by cells but slightly, if at all, larger than those of 
the ordinary size ; it is usual, however, to find the apices occupied by 
one or several spiniform tubuli often considerably larger than those in 
the intervening spaces, Cells small, somewhat unequal in size, from 
thirteen to fifteen in the length of .! of an inch. The cell-walls are 
moderately thin between the angles of junction of the cells, the majority 
of these being occupied by very large and prominent spiniform tubuli. 
Longitudinal sections show numerous spiniform tubuli, the proper 
tube-walls moderately thin, and no diaphragms. The tubes are at first 
inclined, but soon bend upward and proceed in a direct line to open at 
the surface. 
In tangential sections the cell walls between the numerous spiniform 
tubuli, are quitet hin, and occasionally preserve in a faint manner the 
divisional line between adjoining cells. The walls are somewhat thicker, 
and the spiniform tubuli larger than ordinary, in the groups of cells 
occupying the monticules at the surface. 
This species does not resemble either P. gregaria, or P. petechialis, 
very closely, differing from both of those species in having distinct 
monticules and more conspicuous spiniform tubuli. P. petechialis 
forms very small conical zoaria, never, so far as I have been able to 
observe, more than .12 of an inch in diameter. Its vertical range is 
extended, I haviny collected typical specimens in the Upper Trenton 
rocks of Kentucky, and at nearly all elevations in the Cincinnati group. 
The range of P. asperula is much less extended, being apparently 
restricted to the strata between 300 and 450 feet above low water mark 
in the Ohio river. 
