CORALS AND BRYOZOA. 
265 
This is one of the most common and characteristic species and will be readily 
distinguished from any other form. The triangular branches, with their alate 
marginal extensions, present so different an aspect from the ordinary flattened 
forms of this species that the name Pteropora was suggested for them. In 
this direction also these forms approach Prismopora, and it may yet be found 
desirable to unite the different modifications under one generic term. 
Formation and localities. Hamilton group, Montieth’s Point, Ontario county; 
Bellona, Yates county; West Hamburg, Erie county; UnadillaForks; Borodino, 
Onondaga county ; near the head of Canandaigua lake ; near Arkona, Bosanquet 
Township, Ontario, Canada, and numerous other localities. 
PRISMOPORA, Hall. 1881. 
(See page 97.) 
Prismopora dilatata. 
PLATE LXII, FIGS. 13, U. 
Prismopora dilatata, Hall. Trans. Albany Institute, vol. x, p. 193. 1881. 
“ “ “ Report of State Geologist for 1883, p. 50. 1884. 
Zoarium ramose, proceeding from a spreading base, which for the space of a few 
mm. above is nearly cylindrical, with a diameter of about 3 min., then 
rapidly expanding; the frond is apparently bifurcated and also laterally 
branched; branches generally triangular, sides unequal, two of them very 
concave, sub-angular, the other much less concave; on one branch measured 
the width of each of two sides is 3 mm., of the third side 5 mm.; some of 
the branches are larger than this, and others smaller, but generally preserv¬ 
ing about the same proportions; margins slightly diverging; non-celluli- 
ferous marginal space about .50 mm. in width; below each bifurcation and at 
the angles formed by two branches there is an elongate, triangular space 
1 mm. wide and 3 mm. long, destitute of cell apertures; bifurcation and 
lateral branching frequent, occurring at intervals of from 8 to 10 mm.; the 
lateral branches are both alternating and opposite. Cells tubular, arising 
from mesial plates, which radiate from the center to each angle of the 
branch. Intercellular tissue composed of irregularly disposed vesicles. Cell 
