HAMILTON GROUP. 



DESCRIPTIONS OF SPECIES. 



TREMATOPORA, Hall. 1852. 

 Tbematella, s. g., Hall. 1886. 



(See pages lo and 69.) 



Tbematopora (Tbematella) pebspinulata. 



NOT KIGtRKD. 



IVematopora perspinidata, 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 flat, 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. 



