NIAGARA FALLS AND VICINITY 



173 



tions; zooecia subtubular, more or less oblique, radially arranged 

 about a central axis and opening on all sides of the segments. 



Helopora fragilis Hall (Fig. 74) _,_-..^__ __ 



(1852. Pal. N. Y. 2:44, pi. 18, fig. 3a-f) [ / . — } 



Distinguishing characters. Minute 

 cylindric or clavate zoarium swollen 

 at one end; oval or subangular pores, 

 having a spiral direction around the 

 stipe and arranged between longi- 

 tudinal elevated lines. 



Found in the Clinton beds at Lock- 

 port etc. (Hall). Probably occurs also at Niagara. Also abundant 

 in the thin calcareous upper Medina layers at Niagara (?). 



^"-lajjafj. 



Fig. 74 Helopora fragilis natural size 

 and enlarged 



Genus clathropora Hall 



[Ety.: clathri, a lattice; poms, a pore] 



Zoarium composed of anastomosing branches, forming a regular 

 network with round or oval spaces or fenestrules, with a pointed. 





/._.. 



.i^* 



I'M 



/' 



Fig. 75 Clatliropora frondosa with portions of cellulif erous face enlarged 



articulating base ; the branches are made up of two layers grown to- 

 gether back to back, and with the zooecial tubes opening on both 

 sides of the frond; apertures usually subquadrate, arranged longi- 

 tudinally. 



