74 PALEONTOLOGY OF NEW YORK. 



ACANTHOCLEMA TRISEBIALE. 



PLATE XXVIII, FIGS. 5, «. 



StietoporatrUertalig,BkJ.x.. Report of State Geologist for 1882. Kxjil. pi. 25 (xxviii), figs. 5, 6. 1883. 



ZoARiUM ramose, solid ; diameter .50 mm. ; bifurcations infrequent. Cell aper- 

 tures oval, length 15 mm., width from one-half to two-thirds the length ; 

 disposed in longitudinal parallel rows ; six rows in the circumference of a 

 branch, separated by comparatively prominent ridges. 



This species may be distinguished by its slender branches, and minute cell 

 apertures. 



Formation and locality. Upper Helderberg group, near Caledonia, N. Y. 



N EM AT AXIS, Hall. 1886. 

 Nemataxis fibrosds. 



PLATE XXV, FIGS. 80-36. 

 NeiiuUaxlt fibrosa. Hall. Report of State Geologist for 1885, ailvance sheets. Expl. pi. 2.">, figs. 30-36. 1886. 



ZoARiUM ramose, solid; branches 4 mm. in diameter; bifurcations comparatively 

 frequent. Cells tubular, polygonal, arising from a central filiform axis, 

 diverging at an angle of forty-five degrees until within a short distance 

 from the surface, when they abruptly turn outward. Cell walls in con- 

 tact for nearly their entire length. Cell apertures oval, length .30 mm., 

 width about one-half the length ; clo.sely disposed in longitudinal parallel 

 rows, separated by prominent ridges ; about thirty rows on a branch : per- 

 istomes very thin, slightly elevated. At intervals of 3 mm. the surface is 

 marked by monticules which are destitute of cell apertures, and extend across 

 the branch, giving it an annulated appearance. The cell apertures are 

 frequently obsolete, the surfjujes being occupied by prominent longitudinal 

 ridges. 



In a fractured specimen, near the base, exposing the interior below the sur- 

 face, the stipe exhibits a compact fibrous texture. 



Formation and locality. Upper Helderberg group, Ontario, Canada. 



