86 PALEONTOLOGY OF NEW YORK. 



cell walls, extcmling partially across the tube. Apertures paliform, diameter 

 .20 mm. ; very closely disposed, frequently in diagonally intersecting rows, 

 the surfiice presenting a reticulated appearance. Surface between apertures 

 elevated, forming ridges ; frequently a prominent node at the intersection of 

 the ridges, sometimes a depression or pit. Surface with prominent monti- 

 cules, which are transversely in contact, and longitudinally distant about 2 

 ram., giving to the frond an anuulated appearance. Intercellular structure 

 vesiculose. 



Formation and locality. Upper Helderberg group. Falls of the Ohio river. 



SELENOPORA, s. G., Hall. 1886. 



LiCHENALIA (SeLENOPORA) CIRCINCTA. 

 PLATE XXV, FIGS. 13-16. 



lAchenalia circincta, Hall. Trans. Albany Institute, vol. x, abstract, p. 11. 1881. 



SeUniipora " " Report of State Geolog-ist for ISS.'i, advance sheets. Expl. pi. 25, figs. 



13-13. 1886. 



ZoARiUM consisting of very thin lamellate expansions, encrusting other objects. 

 Cells oblique, frequently alternating and imbricating. Apertures circular or 

 broadly oval, diameter .10 mm.; anterior margin of peristome slightly ele- 

 vated ; posterior portion strongly elevated, denticulated, projecting over and 

 partially concealing the opening. The posterior portions of the peristomes 

 are connected by oblique walls which traverse the surface between the aper- 

 tures, uniting and forming polygonal vestibular areas. Maculae distant from 

 each other 4 mm., consisting of circular spaces, destitute of apertures, having 

 a diameter slightly less than 1 mm. ; the cells immediately adjacent, radiating 

 from them, being larger and more oblique than on other portions of the frond. 



This species may be distinguished from S. complexa by its much smaller cell 

 apertures and vestibular areas. 



Formation and locality. Upper Helderberg group, Falls of the Ohio river. 



