182 
PALAEONTOLOGY OF NEW YORK. 
This species most nearly resembles T. (0.) regularis of the Lower and 
Upper Helderberg groups, but the branches are usually more slender, the cell 
apertures are proportionally larger and more conspicuous, and there are 
usually fewer ranges of apertures on a branch: from T. (0.) tortalinea it may 
be distinguished by its more rigid appearance, the more prominent and 
straighter longitudinal ridges; when the frond is worn or macerated the 
longitudinal, parallel arrangement of the cell apertures is preserved, while 
in that species the obliquely transverse arrangement is the most conspic¬ 
uous : from Acanthoclema sulcatum it may be distinguished by the fewer ranges 
of cell apertures on a branch, by the rounded ridges separating the apertures, 
and the flattened surface between the ridges: from T. (0.) carinata it may 
be distinguished by its smaller size, smaller, more distant cell apertures, and 
the absence of nodes between the apertures: from A. Hamiltonense it is 
distinguished by its smaller size, fewer ranges of apertures on a branch, 
and the absence of minute pits between the cell apertures: from T. (0.) 
bispinulata by its smaller size, fewer ranges of apertures, more prominent, 
rigid, longitudinal ridges, and the absence of nodes between the cell apertures. 
Formation and locality. Hamilton group, Darien Centre, Erie county, N. Y. 
Trematopora (Orthopora) bispinulata. 
PLATE LV, FIGS. 27-30 ; AND PLATE LVI, FIGS. 16-18. 
Callopom bispinulata. Hall. Trans. Albany Institute, vol. x, p. 182. 1881. 
“ “ “ Report of State Geologist for 1883, p. 14. 1884. 
Bryozoum ramose, solid; bifurcations infrequent; branches diverging at an 
angle of forty-five degrees, diameter from 80 to 1.25 mm., enlarging and 
becoming a little flattened before bifurcation. Cell apertures tubular, arising 
from the center of the branch, oblique to the axis for about one-lialf their 
length, and then abruptly bent toward the surface. Cell apertures oval, 
length about .25 mm., width from one-third to one-half the length, usually 
disposed in longitudinal lines, frequently alternating and forming oblique, 
transverse rows, sometimes somewhat irregularly disposed; distant longi¬ 
tudinally the diameter of an aperture. Rows of apertures separated by more 
