192 PALEONTOLOGY OF NEW YORK. 



delicate appearance. When well preserved this species does not resemble A, 

 scutulatum, but when worn or m.icerated it sometimes presents a similar 

 appearance, the inter-apertural pits being obsolete, and the ridges nearly or 

 quite in contact between the cell apertures ; but it is always without the 

 node at the junction of the ridges, which is a characteristic feature of that 

 species, from A. alternatum, of the Upper Helderberg group, it may be distin- 

 guished by its inter-apertural pits, and from T. (0.) regularis, of the Lower and 

 Upper Helderberg groups, by its larger cell apertures and the presence of inter- 

 apertural pits. 



Formation and localities. Hamilton group, West Hamburg, Erie county, 

 and near New Berlin, N. Y. 



ACANTHOCLEMA SULCATUM, n. Sp. 

 PLATE LV, FIG. 7 ; PLATE LVI, FIG. 7. 



ZoARiUM ramose, solid ; bifurcations comparatively infrequent; branches widely 

 diverging, diameter about .50 mm. Cells tubular, arising from a filiform 

 axis at the center of the branch, in contact for the greater portion of their 

 length. Cell apertures oval, length .20 mm., width about one-half their 

 length, disposed in longitudinal parallel rows, distant more than the 

 length of an aperture ; six rows on a branch, separated by very prominent, 

 angular, granulo.se ridges ; the surface between the ridges is concave, giving 

 to the cell apertures the appearance of being situated in channels. Peri- 

 stomes very thin, scarcely elevated. 



This species most nearly resembles Acanthoclema triseriale of the Upper Helder- 

 berg group, but may be distinguished as follows : the branches are somewhat 

 more slender, the longitudinal ridges are more prominent, the cell apertures are 

 much smaller. From Trematopora {Orlhopora) regularis it may be distinguished 

 by the more prominent, angular, longitudinal ridges, the comparatively larger 

 cell apertures, and the concave surface between the longitudinal ridges ; nearly 

 the same features distinguish it from T. (0.) tortalineu: from Acanthoclema 

 alternatum of the Upper Helderberg it is distinguished by its angular ridges and 

 absence of nodes between the cell apertures. 



Formation and locality. Hamilton group, near Canandaigua Lake, N. Y. 



