244 



Cincinnati Society of Natural History. 



or less numerous, but never conspicuous, and developed at the angles 

 of junction of the cells, or in the substance of their walls. 



In its typical form this species may be readily distinguished from 

 the preceding by its tuberculated surface. The more nearly smooth 

 examples can be distinguished by the thicker cell walls, stellate macu- 

 la?, and much more flattened branches of H. curvata. 



Formation and locality: Cincinnati group. Rather common near 

 the tops of the hills at Cincinnati, O. 



Peronopora uniformis, n. sp. (Plate X., figs. 8, 8a.) 



Zoarium composed of erect, flattened, smooth, and undulating ex- 

 pansions, of several inches in height, varying in thickness from one to 

 nearly three tenths of an inch ; composed of two layers of cells, grow- 

 ing in opposite directions from the median plate, which is double, and 

 constituted by the adhesion of their epithecal lamina?. The cells are 

 polygonal, subequal, and thin-walled, with an average diameter of 

 about y^Q-th of an inch. Interstitial cells are almost entirely wanting, 

 being usually restricted to small, insignificant clusters, or irregularly 

 scattered among the proper cells. 



In a longitudinal section (Plate X., fig. 8) the tubes at first are 

 thin- walled, and lie prostrate upon the flexuous median lamina; but 

 they soon bend outward and proceed straight to the surface, their 

 walls becoming at the same time moderately thickened; a few are 

 crossed throughout their length by only straight diaphragms, while in 

 the greater number, they are nearly wanting, and instead, a closely 

 arranged series of large cystoid diaphragms lines one of the walls. 

 The diaphragms in the interstitial tubes are crowded. 



In tangential sections (Plate X., fig. Sa) the tubes are polygonal, 

 the walls of moderate thickness, and the interstitial tubes are almost 

 entirely absent, and never present in great numbers. The spiniform 

 tubuli are comparatively few and small, and usually only developed at 

 the angles of junction of the tubes. 



The general outward appearance of the zoarium of this species is in 

 all respects like that of P. decipiens, Rominger. By the aid of a 

 magnifier, P. uniformis may be readily enough distinguished from 

 that species by its thinner walls and very few interstitial tubuli. 

 Peronopora compressa, Ulrich, is a small species, also with thin-walled 

 cells. It differs, however, from P. uniformis, in having numerous 

 interstitial tubes, and a great number of well developed spiniform 

 tubuli. 



