188 PALjEONTOLOGY OF NEW YORK. 



across the cavity : from T. (0.) interplana it may be distinguished by its larger 

 branches, more elongate cell apertures, and the narrow intermediate space ; 

 from all other species of this geological formation it may be distinguished hy 

 the comparatively prominent nodes surrounding the cell apertures. 



Formation and locality. Hamilton group, West Hamburg, Erie county, N. Y. 



Trematopora (Orthopora?) orbipora. 



PLATE LV, KIGS. 13, 14 ; AKD PLATE LVI, KIG. 8. 



Trematopora orbipora. Hall. Trans. Albany Institute, vol. x, p. 181. 1881. 



Report of State Geologist for 1883, p. 12. 1884. 



Zoaricm ramose ; bifurcations infrequent ; branches widely diverging. Cells 

 tubular, arising from the center of the branch, increasing by interstitial 

 addition, in contact for the greater portion of their length, abruptly bending 

 outward and separating near the surface ; walls very thin ; septa thin, in- 

 frequent, in many of the cells entirely wanting. Cell apertures broadly oval, 

 frequently circular, length .38 mm., width usually about three-fourths the 

 length, but on some fronds not more than one-half, very closely and usually 

 irregularly disposed, but occasionally forming indistinct, oblique transverse 

 rows ; the peristomes are sometimes obsolete, and the surface between the 

 apertures is elevated, angular or rounded, with numerous minute nodes ; 

 at other times the peristomes are moderately strong and equally elevated, with 

 minute nodes, the surface between the apertures is flat or slightly concave, 

 and in some specimens apparently with very small pits. The nodes in the 

 course of growth form minute tubuli between the cell tubes near the surface. 

 The internal characters of this form are the same as those of the species 

 included under the sub-genus Orthopora, though some of the fronds have 

 their cell apertures irregularly disposed, others have them regularly arranged 

 in oblique transverse rows. I have, therefore, concluded to place it under this 

 sub-genus, although the external characters of some of the fronds are similar 

 to those of the sub-genus Trkmatella. 



This species most nearly resembles T. (0.) transversa, but may be distinguished 

 by the larger, more nearly circular cell apertures, their more irregular dispo- 



