CORALS AND BRYOZOA. 191 



and the prominent nodes at the junction of the longitudinal ridges ; from all 

 other species, of this geological formation, by the strong, longitudinal ridges, 

 which coalesce between the apertures, and the prominent conical nodes at the 

 points of junction. 



Formation and locality. Hamilton group, York, Livingston county, N. Y. 



ACANTHOCLEMA HaMILTONENSE. 



PLATE LV, FIGS. 18-3B. 



Ceriopnraf BamiUonensia, Nicholson. Geological Magazine, April, 1874. 

 Caltopora " Hall. Ti-ans. Albany Institute, vol. x, p. 182. 1881. 



" bipiinctala, " Report of State Geologist for 1883, p. 1.5. 1881. 



ZoARiUM ramo.se, solid ; bifurcations infre(|uent ; branches diverging at an angle 

 of from fifty to ninety degrees, diameter about .75 mm. Cells tubular, 

 arising from a filiform axis at the center of the branch, a little oblique to 

 the surface, and .slightly curved. Cell apertures oval, length .20 mm., width 

 from one-half to two-thirds the length, usually disposed in longitudin.al, 

 parallel rows, frequently alternating and forming oblique, transverse rows ; 

 sometimes, on portions of the frond, they are somewhat irregularly disposed. 

 Peristomes thin, scarcely elevated. The longitudinal ranges of apertures 

 are separated by prominent ridge.-*, which are sometimes straight, but 

 usually slightly sinuous, freij-uently approaching e.ich other between the 

 apertures, but rarely in contact. In the transverse space between the 

 apertures there are usually two small, usually quadrangular pits, generally 

 situated one above the other ; when the cell apertures are irregularly 

 arranged, they are occasionally entirely surrounded by these pits ; a small 

 node also often occurs at the base of each aperture, and .sometimes at each 

 end of the aperture, obscuring the pits. These pits in the course of growth 

 form minute, curved tubuli between the cell apertures. 



This species most nearly resembles Trematopora (Orthopora) bispinulata, both 

 species having the cell apertures disposed in longitudinal ranges separated by 

 ridges, but the ridges of this species are much more prominent and regular, 

 and the surface is marked by inter-apertural pits ; the frond has also a more 



