98 PALEONTOLOGY 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. 



Prismopora paucirama. 



PLATK XXVUI, KIU. II ; anu PLATE XXIX, FIGS. 18, 17. 



Prismopora paucirama. Hall. Trans. Albany Institute, vol. x, abstract, p. 17. 1881. 



Report of State Geologist for 1883. 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 mm.; 

 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; dispo-sed 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. 



