246 Cincinnati Society of Natural History. 
together, there being no sharply defined lines of contact, though these 
are rather faintly indicated by an irregular and often confused central - 
zone, of lighter color than that portion of the walls immediately sur- 
rounding the visceral cavity of the tubes. Their structure is on the 
whole quite like that of species uf Monticulipora, but more like that 
of some species of Amplexopora (e. g., A. septosa, Ulrich, and A. 
—moniliformis, Nich.) 
Figures 2 and 2a, on the same plate, represent typical sections of 4. 
maculata. Comparing fig. 2 with fig. 1, both representing tangential 
sections, cutting the zoarium just below the suriace, we find that, with 
the exception of the relative thickness of the cell-interspaces or walls, 
the two species are precisely alike. In both we find the same peculiarly 
constructed “macule,” while in the minute structure of the cell-walls 
no difference whatever is manifest.. In their vertical sections a corre- 
sponding agreement of structure is apparent. So far as I have been 
able to ascertain, the layers of the zoarium of A, hirsuta never attain 
~ more than perhaps one half the thickness of a fully matured layer of 
A. maculata, while on the other hand, the cell walls of the former are 
usually about twice as thick as those of the latter. Aside from these 
specific points of difference, they agree in having remote horizontal 
diaphragms, and similarly constructed “macule.”’ The latter are di- 
vided by more or less distinct floors, having an upward curvature, cor- 
responding to the convexity of the outer or exposed portion of the 
elevated “macule.” Not infrequently, on the upper side of these 
floors, some conical hollow projections may be detected, which doubt- 
lessly represent modified spiniform tubuli, or structures of similar 
value. These do not appear to be continuous from one floor to the 
other, but the evideuce at hand seems to establish as a facet, that each 
series is separately developed at the successive stages of growth. 
Further, in many specimens the zoarium is divided into three, rarely 
four, distinct layers, of very nearly equal thickness, separated from 
each other by parallel bands of sclerenchyma, that, usually, do not 
seriously interrupt the further growth of the zoarium, not the direct 
sequence of the cells. | 
Of the other forms originally referred by me to Atactopora, I now 
feel satisfied that A. mundula, A. multigranosa, A. tenella, and A. 
ortont, Nicholson, belong to an entirely distinct genus. To this list I 
add three new species, so that the genus as at present known, is rep- 
resented by at least seven distinct species. All of these are from the 
Cincinnati group, in which the genus is found to range throughout 
