é American Paleozoic Bryozoa. 251 
surface markings, the zoarium of A. typicalis being prevalently en- 
tirely smooth, while that of A. newportensis is generally strongly tu- 
berculated, besides being of more robust growth. The cell apertures 
also are never so distinctly petaloid as in the type species. 
The relations between Atactoporella and Trematopora, suggested by, 
such a specimen as is represented by figure 4, on Pl. XII., will be dis- 
cussed a few pages hence, under the emended definition of that genus. 
Formation and locality : Cincinnati group. I have examined about 
twenty-five specimens of this species, all of which were obtained from 
the shaly beds, near the southern line of the city of Newport, Ky. The 
height of these strata is perhaps 125 feet above low water mark in the 
Ohio river. 
ATACTOPORELLA SCHUCHERTI, n. Sp. (Pl. XII, figs. 5-50). 
Zoarium parasitically attached to shells and other foreign bodies, 
over which it forms thin irregular expansions, usually less than an 
inch in diameter, and rarely more than .03 of an inch in thickness. 
The surface generally exhibits at intervals of .1 inch or more, slightly 
raised eminences. When in a good state of preservation (Plate XII, 
fig. 5), the cellular structure is almost entirely obscured by the innumer- 
able surface extensions of the large spiniform tubuli, in many of which 
the perforation at the apex is clearly shown. When worn, the cell 
apertures are rounded, about ten in .l of an inch, with thick inter- 
spaces, occupied by the shallow calices of numerous interstitial cells, 
which in old examples are not readily detected. 
The distinctive characters of the species are well brought out in 
tangential sections (Pl. XII., figs. 5a and 50). The cell walls are thin, 
and between the numerous and large spiniform tubuli, are of about 
equal thickness throughout. Excepting when the section cuts the 
zoarium just beneath the surface, it is difficult to discriminate between 
the interstitial cells and true zocecia. But, when near enough to the 
surface, the former are mostly filled with transparent calcite, while the 
latter are filled with particles of the surrounding matrix, and when this 
fails they may be more certainly distinguished by the possession of the 
crescentic edges of the cystoid diaphragms. The interstitial cells are 
numerous, but very unequal in size ; as a rule, they completely isolate 
the true cells. The arrangement, size and character of the spiniform 
_tubuli are well shown in the figures referred to. 
In vertical sections, unless they follow the direction of the growth of 
the colony, the same difficulty of distinguishing the interstitial from 
