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; Unadilla Forks; Borodino, 

 Onondaga county ; near the head of Canandaigua lake ; near Arkona, Bosanquet 

 Township, Ontario, Canada, and numerous other localities. 



PRISMOPORA, Hall. 1881. 



(St'c i>agu 97.) 



Prismopora dilatata. 



PLATE LXII, FIGS. 13, 14. 



Pristnopora dilatata. Hall. Trans. Albany Institute, voL x, p. 193. 1881. 



Report of State Geolog-ist for 1883, p. 50. 1884. 



ZoAEiUM ramose, proceeding from a spreading base, which for the space of a few 

 mm. above is nearly cylindrical, with a diameter of about 3 mm., 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 



