178 
PALAEONTOLOGY OF NEW YORK. 
or polygonal vestibular area; margins of the elevations finely granulose 
and at their angles are comparatively prominent nodes. The surface 
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 
squares, in this condition being very unlike that of a well preserved specimen. 
This species most nearly resembles T. (0.) polygona , 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. 
(0.) ornata it is distinguished 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 vestibular areas. 
Formation and locality. Hamilton group, Darien Centre, N. Y. 
Trematopora (Orthopora) hexagona, n. sp. 
PLATE LV, FIG. S ; and PLATE LVI, FIG. 6. 
This species is very similar to T. (0.) polygona, but the cell apertures and 
vestibular 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. 
