248 Cincinnati Society of Natural History. 
of those species found in that condition, are so variable in shape, that 
they can not be regarded as properly ramose or frondescent. I hold 
that in all truly ramose or frondescent species of the TREPosTOMATA, 
the zoarium is permanently either one or the other, and I have never 
observed such a vacillation of form as pertains to these aberrant 
specimens of the two species mentioned. We have an entirely parallel 
‘ease in Nicholson’s var. molesta of the typically massive species 
Monticulipora mammulata. As I have in another place pointed out, 
that variety usually assumes a frondescent habit of growth, though 
individuals of the variety vary extremely in outward form. All these 
forms differ from truly ramose and frondescent types of the Monticu- 
liporide, in having both cystoid diaphragms and spiniform: tubuli 
already present in the axial region of the zoarium. 
One character of the genus, the importance of which I am at present 
not yet able to estimate, is developed in an unmistakable manner in at 
least the three species, A. multigranosa, A.mundula, and A. ortoni, viz: 
the secondary deposit of sclerenchyma in the interstitial tubes, and 
their partial suppression. In the young stages of these species the 
intertubular spaces are much thicker than they are in the fully matured 
stage, and the mouths of the interstitial cells can often be detected. 
Sections prepared from fully matured examples, demonstrate that the 
interstitial tubes in the deeper levels of the zoarium are open, and of 
considerable size, their diameter often equaling that of the proper 
zocecia. As growth proceeds, the interstitial spaces are narrowed, 
and a deposit of sclerenchyma around the outer side of the true zocecia, 
cradually fills them up, until in the fully matured state they can 
scarcely be detected any longer. Among the Monticuliporide I am — 
not acquainted with any form, excepting, perhaps, Trematopora, in 
which a similar filling up of the interstitial cells occurred. Among 
the Fistuliporide, however, a similar condition is often present, but 
how nearly they may be due to the same causes, I am not prepared to 
say. 
ATACTOPORELLA TYPICALIS, n. sp. (PI. XII, figs. 3-3d). 
Zoarium, in its typical condition, forming thin parasitic expansions 
over other bryozoa, having a thickness rarely exceeding .03 of an inch, 
and then only by the addition of another layer. A few specimens are 
lobate, and by an excessive development of the lobes, they have become, 
to a small extent, subramose. At rather unequal intervals, averaging 
perhaps .1 inch, the surface exhibits groups of cells slightly larger 
