CORALS AND RRYOZOA. 
73 
The characteristic features of the surface are the longitudinal ridges alter¬ 
nating with the rows of nodes. 
Formation and locality. Upper Helderberg group, Onondaga Valley, N. Y. 
Acanthoclema ovatum. 
PLATE XXVIII, FIG. 3. 
Trematopora, sp. undt., Hall. Report of State Geologist for 1882. Expl. pi. 25, fig. 3. 1883. 
Zoarium ramose, solid; diameter 1 mm.; bifurcations infrequent. Cell aper¬ 
tures oval, length .22 mm., width one-half the length; disposed in longi¬ 
tudinal parallel rows; twelve rows in the circumference of a branch, separated 
by narrow, slightly elevated ridges. 
Formation and locality. Upper Helderberg group, Onondaga Valley, Onondaga 
county, N. Y. 
Acanthoclema divergens. 
PLATE XXVIII, FIG. 2. 
Trematopora? sp. undt., Hall. Report of State Geologist for 1882. Expl. pi. 25, fig. 2. 1883. 
Zoarium ramose, solid; branches .60 mm. in diameter, diverging at an angle 
of ninety degrees; bifurcations infrequent. Cell apertures oval, length .24 
mm., width about one-half the length; disposed in longitudinal parallel 
rows; six rows in the circumference of a branch, separated by narrow, 
slightly elevated ridges. 
This species closely resembles A. triseriale, but the cell apertures are pro¬ 
portionally much larger. A critical comparison shows this form to be quite 
distinct from the preceding (A. ovatum ), with which it had been united in the 
previous descriptions. 
Formation and locaity. Upper Helderberg group, Onondaga Valley, Onondaga 
county, N. Y. 
