American Paleozoic Bryozoa. 247 
the formation. The range of each species is however very restricted, 
being in perhaps no case more than one hundred feet, and usually 
much less. The genus may be characterized as follows: 
ATACTOPORELLA, 0. gen. 
o, sometimes lobate, rarely sub-ramose, and 
generally composed of several superimposed layers. Surface always 
presenting more or less distinct groups of cells siightly larger, or with 
wider interspaces than the average, which usually occupy the slopes of 
more or less elevated, rounded or conical, monticules. Zocecia tubular, 
rounded, with more or less distinctly petaloid apertures, due to the in- 
flection of the thin walls, by the numerous spiniform tubuli. Intersti- 
tial cells numerous, angular, often completely isolating the true cells. 
As the layers become mature they are usually filled between the 
crowded horizontal diaphragms, by a deposit of sclerenchyma. Beside 
a limited number of straight diaphragms, nearly all of the proper 
zocecia are provided with a series of cystoid diaphragms. 
Type, Atactoporella typicalis, n. sp. 
As may have been gathered from the above description, the new 
genus differs from Atactopora, as before restricted, in having numerous 
closely tabulated interstitial cells, cystoid diaphragms in the proper 
zocecia, and thin, instead of thick walls. These are all good generic 
characters, and serve to remove the genus perhaps farther from 
Atactopora proper, than from either Monticulipora or Peronopora. 
Monticulipora differs in having no true interstitial cells, while the 
spiniform tubuli are mainly restricted to the angles of the cells, and 
only very rarely inflect the tube-walls. In Peronopora, however, we 
have a nearer ally, and it is unquestionable that the true affinities of 
Atactoporelia lie in that direction. In both we have interstitial cells, 
spiniform tubuli, and cystoid diaphragms. On the other hand, the 
difference in their habits of growth, the zoarium of Peronopora being 
-doubled-leaved, and perhaps, occasionally, frondescent, while that of 
Atactoporellia is constantly more or less p&rasitic, the thicker and 
somewhat differently constructed cell-walls, and less numerous spini- 
form tubuli of Peronopora, are characters that serve to distinguish 
all the species of the two genera so far known. I can not admit that 
the fact that the zoarium of both A. typicalis, and A. newportensis, 
occasionally assumes a sub-ramose character, in any way nullifies the 
point of difference in growth, regarded by me as one of the characters 
separating the proposed genus from Peronopora, The few specimens 
Zoaria usually incrusting 
