98 
PALAEONTOLOGY OF NEW YORK. 
thickness about .80 mm. ; bifurcations very frequent. Cells tubular, arising 
from a mesotheca which extends from the center of the branch to each 
angle. For one-half the length the cell tubes are nearly parallel with the 
mesotheca, then turn abruptly outward. Apertures trilobate, frequently 
papillate, length .24 mm., width slightly less; radiating upward from the 
center of each face to the margin; usually disposed in more or less regular 
longitudinal rows, the longitudinal disposition being the more strongly marked 
near the middle of the branch, sometimes irregularly disposed. Rows some¬ 
times separated by comparatively prominent ridges Peristomes sometimes 
equally elevated, but usually the posterior margin is the more strongly 
elevated, having two denticulations. Intercellular space vesiculose, vesicles 
small and of irregular size. 
This species may be distinguished from P. paucirama by the much more fre¬ 
quent bifurcations. 
Formation and locality. Upper Helderberg group, Falls of the Ohio river. 
PllISMOPORA PAUCIRAMA. 
PLATE XXVIII, FIG. 11 ; and PLATE XXIX, FIGS. 16, 17. 
Prismopora paucirama, Hall. Trans. Albany Institute, vol. x, abstract, p. 17. 1881. 
“ “ “ Report of State Geologist for 18S2. Expl. pi. 25, fig - . 11. 1883. 
“ “ “ Report of State Geologist for 1885, advance sheets. Expl, pi. 29, figs. 
16, 17. 1886. 
Zoarium ramose ; branches triangular, prismatic ; two of the faces equal, width 
2.75 mm., width of the third 4 mm., concave; greatest thickness 1.20 nun.; 
bifurcations occur at intervals of 20 mm. or more. Cell apertures oval or 
trilobate, sometimes nearly circular, length from .20 to .25 mm., arranged in 
lines parallel with the axis, smallest at the middle of the branch, gradually 
growing larger and diverging, until at the margin they are at right angles to 
the axis; disposed in longitudinal and oblique ascending rows, which diverge 
from the middle of the branch: peristomes strong, the posterior portion 
elevated slightly more than the anterior. 
Formation and locality. Upper Helderberg group, Thomson’s lake, Albany 
county, N. Y. 
