18 PALjEONTOLOGY OF NEW YORK. 



tion. At each end of the aperture and frequently on other portions of the 

 n>ar<;in there is a short obtuse spinule. Interapertural space concave. 



This species, in its arrangement of cell apertures, is very similar to T. rhom- 

 biftra, but differs from that species in having the apertures much more distinctly 

 oval, and more widely separated, and in the concave interapertural space. 



Formation and locality. Lower Helderberg group, near Clarksville, N. Y. 



Trematopora (Ortiiopora) rhombifera. 



PLATE XI, FIGS. IS, 17-20; ANU PLATE XXUI, FIGS. U, 12. 



TretiuUopnra rhtnnb\fera. Hall. Twenty-sixth Rept. N. Y. State Mus. Nat. Hist., p. 103. 1874. 



Thii-ty-second Rept. N. Y. State Mils. Nat. Hist., p. l.')2. 1879. 

 In part Treinato]xnra rJlombi/era, Hall. Report of St.-itc Geologist for 1883 Expl.pl. 11, figs. 15-20. 1883. 



ZoARiu.M ramose, solid, diameter of branches from .50 to 2 mm. Cells tubular, 

 arising from the center of the branch, rapidly diverging till within a short 

 distance of the surface when they turn more abruptly outward. Apertures 

 oval or, occasionally, sub-rhomboidal, length .20 mm., width .12 mm. ; very 

 closely disposed in quincunx order: margins thin, very slightly elevated, 

 granulose; granules often obsolete. Interapertural space generally elevated 

 above the apertures, though sometimes Hat; in well preserved specimens 

 nodose or granulose, occasionally so set with minute spines that the aper- 

 tures are obscured. 



This species, in some points, is closely allied to T. regularis, with which it is 

 often associated, but differs materially in the arrangement of the cell apertures, 

 that species having the apertures in longitudinal lines with a prominent ridge 

 between, while in this species they are always spirally arranged. In worn 

 specimens the difference is less distinctly seen. 



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

 group, near Clarksville, Albany county, and at Schoharie, N. Y. 



