CORALS OF THE CINCINNATI GROUP. 221 



confounded for a moment, the former constituting large masses of scarcely 

 separate corallites, which vary from one to six lines in diameter. 



Position and locality : Cincinnati group, Cincinnati, Ohio. Collection of Mr. U. P. 

 James. 



Genus PROTAREA., Edwards and Haime. 



(Compt. Rend., T. XXIX., 1849.) 



Protarea vetusta, Edwards and Haime. 



Pontes? vetusta, Hall ; Pal. N. Y., Vol. I., p. 71, pi. 25, flgs. 5a, 56, 1847. 



Astricopora vetusta, D'Orbigny ; Prodr. de Paleont., 1850. 



Protarea vetusta, Edwards and Haime; Pol. Foss. des Terr. Palseoz., pi. 14, fig. 6. 



Corallum forming thin crusts, about one-third of a line in thickness, 

 which grow parasitically upon foreign bodies. Calices nearly equally 

 developed, usually hexagonal, about one line in diameter or rather less, 

 shallow, the bottom of the cup being tuberculated. Septa twelve in 

 number, sub-equal, extending but a short distance inwards towards the 

 center of the visceral chamber. Walls of the calices thick. 



This pretty little coral forms thin crusts upon species of Strophomena, 

 Pleurotomaria, and other fossils, and there appears to be no reason to 

 doubt its identity with the specimens described by Hall from the Tren- 

 ton limestone. The form described from the Silurian rocks of Ohio, by 

 Milne Edwards and Haime, under the name of Protarea Verneuilli, is 

 chiefly distinguished from this by the slightly larger sizes of the calices, 

 but I have seen no specimens that I could refer to it. 



Position and locality ■• Cincinnati group, near Cincinnati, Ohio. 



Genus TETRADIUM, Dana, 1846. 



(Zooph., Vol. VIII., p. 701.) 



"Coralla massive, consisting of four-sided tubes and cells, with very 

 thin septa or parietes ; cells stellate, with four narrow laminae." 



"This genus is near Receptaculites, but differs in having very thin 

 parietes and four distinct rays between the cells, one to each side. The 

 specimen answering to the description is a fossil of uncertain locality in 

 the collections of Yale College, New Haven. The cells are about half a 

 line in breadth." (Dana, loc. cif) 



To this definition Prof. J. M. Safford (Amer. Journ. Sci. and Arts, 2d 



