16 PALEONTOLOGY OF NEW YORK. 



mm. Tlirouf^h the thickening of the cell walls near the surface the apertures 

 are constricted and oval in outline. The inter-apertural spaces are strongly 

 elevated, frequently forming irregular ridges, the surfiice then resembling, 

 in miniature, the roughened bark of a tree. 



This species is easily recognized by its polygonal cell tubes, oval apertures, 

 it« peculiarly roughened surfjice and the widely diverging branches. 



Formation and localitij. In the shaly limestone of the Lower Helderberg 

 group, near Clarksville, N. Y. 



NoTB.— This form tloes not fully represent the charactei-s of Trbmatblla, but I prefer to leave it for the 

 present under that deslg^iation. 



Orthopora, n. s. g. 



ZoARiUM ramose, cell apertures arranged in parallel, longitudinal rows. Inter- 

 cellular space solid, or occupied near the surface, by minute tubuli, destitute 

 of septa. 



Externally very similar to Rhombopora, but differing internally. These forms 

 differ from Trematella in the regular arrangement of the cell apertures. 



Trematopora (Orthopora) regularis. 



PLATE XI, FIGS. 1-8; PLATK XIII, FIG. 1-3; AND PLATE XXIII, FIG. I. 



Tremaloimra regularis. Hall. Twenty-sixth Re)it. N. Y. State Mus. Nat. Hist., p. lOtJ. 1874. 



Thirty-second Kept. N. Y. State Mus. Nat. Hist., p. l.^jl, 1879. 

 In p»rt Trematopora reffularis, Hall. Report of State Geologist for 1882. Expl. pi. 11, figs. 1-8; pi. 13, 



figs. 1-3. 1883. 



ZoARiUM ramose, solid; bifurcations infrequent; branches widely diverging, 

 slender, the diameter seldom exceeding 1 mm. Branches having a diameter 

 of only .50 mm. are not uncommon. Cells tubular, arising from the center 

 of the branch and gradually diverging till within a short distance of the 

 surface, when they turn quite abruptly outward. Near the center of the 

 branch the cells are in contact and frequently sub-polygonal from mutual 

 pressure, separating as they approach the surface. Aperture.s elongate-oval, 

 length from .15 to .18 mm., width from one-fourth to one-half the length ; 

 arranged in longitudinal parallel rows, fifteen in the space of five mm.; from 



