CORALS AND BRYOZOA. 283 



The concave central space, lying between the ridges of apertures, and be- 

 tween the zoaria forming the colony, is buUate ; the bullag in the central space 

 have a diameter of from .15 to .25 mm. and are polygonal; those between 

 the ridges are much smaller, having a diameter of from .6 to .10 mm. ; those 

 between the individual zoaria are of two kinds, one circular or sub-polygonal 

 from mutual pressure, the diameter generally from .50 to .60 mm., rarely a 

 little more ; these are very frequently in contact, and when separated the 

 space between them is occupied by bullae similar to those between the 

 celluliferous ridges. When the surface becomes worn the upper walls of the 

 bullae or vesicles are worn or broken away, they have the appearance of 

 shallow pits. 



This genus isvery similar to some forms of the genera Radiopora, or Actino- 

 PORA, of D'Orbigny. (Paleontologie Francaise ; Cretaceous Bryozoa. Plates 

 644 and 649.) 



Formation and localities. Hamilton group, Le Roy, N. Y., and West Williams, 

 Ontario, Canada. 



PTILOPORA, McCoy. 1849. 



Ptilopora striata. 



plate i.xvi, figs. 30-33. 



Ptilcpora Ktriata, Hall. TranR. Albany Institute, vol. x, p. lOli. I8S1. 

 " " " ReiMirt of Stole Geologist for 188:i, p. 58. 1884. 



ZoABiDM consisting of a strong stipe or midrib, proceeding from a spreading 

 base, or from rootlets attached to foreign bodies, and having slender equi- 

 distant lateral branches, connected by slender processes or dissepiments ; 

 celluliferous on one face only. The base of the stipe has a width of 1.50 mm. or 

 more, gradually tapering to .25 mm. ; transverse section circular or broadly 

 oval; lateral branches .25 mm. in width, uniform in size, diverging from 

 the midrib at an angle of about forty-five degrees, regularly distant a little 

 less than twice the width, seven in the space of 5 mm., transverse section 

 broadly oval or circular. 



On the non-celluliferous face the midrib and branches are rounded and 

 striated ; on the lateral branches the striae are of uniform size, five or six 



