188 
PALAEONTOLOGY OF NEW YORK. 
across the cavity: from T. (O'.) interplana it may be distinguished by its larger 
branches, more elongate cell apertures, and the narrow intermediate space; 
from all other species of this geological formation it may be distinguished by 
the comparatively prominent nodes surrounding the cell apertures. 
Formation and locality. Hamilton group, West Hamburg, Erie county, N. Y. 
TrEMATOPORA (ORTHOPORA ?) ORBIPORA. 
PLATE LV, FIGS. 13, 14 ; AND PLATE LVI, FIG. 8. 
Trematopom orbipora, Hall. Trans. Albany Institute, vol. x, p. 181. 1881. 
“ “ “ Report of State Geologist for 18S8, p. 12. 1884. 
Zoarium ramose; bifurcations infrequent; branches widely diverging. Cells 
tubular, arising from the center of the branch, increasing by interstitial 
addition, in contact for the greater portion of their length, abruptly bending 
outward and separating near the surface; walls very thin; septa thin, in¬ 
frequent, in many of the cells entirely wanting. Cell apertures broadly oval, 
frequently circular, length .38 mm., width usually about three-fourths the 
length, but on some fronds not more than one-half, very closely and usually 
irregularly disposed, but occasionally forming indistinct, oblique transverse 
rows; the peristomes are sometimes obsolete, and the surface between the 
apertures is elevated, angular or rounded, with numerous minute nodes; 
at other times the peristomes are moderately strong and equally elevated, with 
minute nodes, the surface between the apertures is flat or slightly concave, 
and in some specimens apparently with very small pits. The nodes in the 
course of growth form minute tubuli between the cell tubes near the surface. 
The internal characters of this form are the same as those of the species 
included under the sub-genus Orthopora, though some of the fronds have 
their cell apertures irregularly disposed, others have them regularly arranged 
in oblique transverse rows. I have, therefore, concluded to place it under this 
sub-genus, although the external characters of some of the fronds are similar 
to those of the sub-genus Trematella. 
This species most nearly resembles T. (0.) transversa, but may be distinguished 
by the larger, more nearly circular cell apertures, their more irregular dispo- 
