HAMILTON GROUP. 
DESCRIPTIONS OF SPECIES. 
TREMATOPORA, Hall. 1852. 
Trematella, s. g., Hall. 1886. 
(See pages 15 and 69.) 
Trematopora (Trematella) perspinulata. 
NOT FIGURED. 
Trematopora perspinulata, Hall. Trans. Albany Institute, vol. x, p. 181. 1881. 
“ “ “ Report of State Geologist for 1883, p. 11. 1884. 
Zoarium ramose, solid; bifurcations infrequent; branches diverging at an angle 
of forty-five degrees, diameter from 1.50 to 3 mm. Cells tubular, apparently 
polygonal, arising from the center of the branch and gradually curving to 
the surface. Cell apertures from elongate-oval to nearly circular, variable in 
size, some having a length of .30 mm., and a width of .15 mm., others are 
nearly circular and have a diameter of about .28 mm., closely and irregularly 
disposed; all intermediate forms occur. Peristomes usually obsolete, and 
when occurring are very slight. Inter-apertural space, sometimes fiat, at 
other times a little elevated and with a very slight striation, occasionally 
granulose. There are numerous, prominent, conical nodes or spinules, 
irregularly disposed, forming a prominent feature of the surface. 
The irregular size and shape of the cell apertures, and the numerous, com¬ 
paratively prominent spinules, will distinguish this species from any other at 
present known, from this geological horizon. 
Formation and locality. Hamilton group, York, Livingston county, N. Y. 
