CORALS AND BRYOZOA. 
215 
Cell apertures circular, diameter .30 mm., irregularly disposed, usually dis¬ 
tant from each other about the diameter of an aperture; apertures usually 
operculate, the opercula rounded or conical at the centers, with five or six 
ridges radiating from the center to the peristomes. Peristomes strong, 
equally elevated, the striations of the cell walls extending over their mar¬ 
gins and giving them a serrulate appearance. Mesopores large, their diameter 
being frequently more than that of the cell apertures; margins slightly 
elevated, and when well preserved granulose. 
Surface marked by low, rounded maculae, the centers of which are distant 
about 6 mm., having a small area occupied by mesopores; the apertures 
immediately adjacent are a little larger than the others, but the difference in 
size is not conspicuous. 
The characteristic features of this species are the opercula, which are well pre¬ 
served in all the specimens seen ; the same feature is also conspicuous in F. oper- 
culata, but this species may be readily distinguished by the smaller size of the 
cell apertures, the equally elevated peristomes, the difference in the character 
of the opercula, and by the mesopores, that species having vesicles between 
the cell apertures: from F. confertipora, it is distinguished by its larger, more 
distant monticules, the more distant cell apertures, the minute serration of the 
peristomes, and the much larger mesopores: from F. variapora by the more 
distant cell apertures, their more nearly uniform size, and the larger mesopores : 
from F. scrobiculata by the prominent monticules, that species having maculae 
not elevated above the surface ; the mesopores and cell apertures are very similar 
in appearance, except that the opercula are rarely present in the cells of the 
latter species. 
Formation and locality. Hamilton group, West Bloomfield, N. Y. 
Fistulipora plana. 
PLATE LVIII, FIGS. 19, 22. 
Thallostigma plana, Hall. Trans. Albany Institute, vol. x, p. 187. 1881. 
“ “ “ Report of State Geologist for 1883, p. 30. 1884. 
Zoarium consisting of thin lamellate expansions, incrusting or free, thickness 
less than 1 mm. No masses formed by the accretion of successive layers of 
