PALAEONTOLOGY OF NEW YORK. 
tion. At each end of the aperture and frequently on other portions of the 
margin there is a short obtuse spinule. Interapertural space concave. 
This species, in its arrangement of cell apertures, is very similar to T. rhom- 
bifera, 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 (Orthopora) rhombifera. 
PLATE XI, FIGS. 15, 17-20; AND PLATE XXIII, FIGS. 11, 12. 
Trematopora rhombifera, Hall. .Twenty-sixth Itept. N. Y. State Mus. Nat. Hist., p. 103. 1874. 
“ “ “ Thirty-second Rept. N. Y. State Mus. Nat. Hist., p. 152. 1S79. 
In part Trematopora rhombifera, Hall. Report of State Geologist for 1S82. Expl. pi. 11, figs. 15-20. 1883. 
Zoarium 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 flat; 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. 
