178 PALEONTOLOGY OF NEW YORK. 



or polygonal vestibular area ; margins of the elevations finely granulose 

 and at their angles are comparatively prominent nodes. The surfhce 

 frequently presents a regularly reticulated appearance. In the process of 

 growth the nodes form minute tubuli between the cell tubes. 



When the surface is worn the longitudinal arrangement of the cell aper- 

 tures is more clearly apparent, the nodes frequently have the appearance of 

 quadrangular pits, and the surface of the frond seems divided into minute 

 squjires, in this condition being very unlike that of a well preserved specimen. 



This species most nearly resembles T. (0.) poli/gona, but may be distinguished 

 as follows : the cell apertures are smaller, proportionally shorter, the polygonal 

 elevations are less elongate, more sharply angular, the granules on the margins 

 are much more minute : from T. (0.) hexagona it is distinguished by its smaller, 

 less elongate cell apertures and much narrower, angular elevations : from T. 

 (O.) ornata it is distinguisiied by its somewhat larger cell apertures, the much 

 narrower, more sharply angular elevations and the absence of prominent nodes, 

 except at the angles of the elevations : from T. (0.) reticulata by the less regu- 

 lar arrangement of the cell apertures and the wider, angular elevations : from 

 Acanthoclema scutulatum by the less elongate and more irregularly disposed cell 

 apertures and the absence of very prominent nodes and pits at the base of the 

 nodes : from T. (0.) rhombifera of the Lower and Upper Helderberg groups, by 

 the broader cell apertures and the less elongate and polygonal vestibuhir areas. 



Formation and locality. Hamilton group, Darien Centre, N. Y. 



Trematopora (Orthopora) hexagona, n. sp. 



PLATE LV, FIG. 8; AND PLATE LVI, FIG. 6. 



This species is very similar to T. (0.) polygona, but the cell apertures and 

 vestibulair areas are somewhat smaller, there are no prominent nodes at the 

 angles of the elevations between the cell apertures, and the granules on the 

 elevations are fewer and more prominent. 



Formation and locality. Hamilton group. Eighteen-mile creek, shore of Lake 

 Erie, Erie county, N. Y. 



