The Rogers Gap Fauna of Central Kentucky 123. 



sized coralla, as in IE, the difference in the size of the coralUtes 

 often is less striking. The vertical corrugation of the walls of 

 the corallites, corresponding to the position of the septa, is shown 

 by Figs. IC, IF. The septa are best indicated in Fig. IE. The 

 base of the corallum was covered by an epithecal layer. In the 

 specimen represented by Fig. IH the epithecal layer was flat, as 

 though tightly pressed against some smooth surface. The base 

 of the initial corallite is seen at the center of the radiating coral- 

 lites, and from this initial corallite others branched off, first toward 

 the right and later toward the left, viewing the corallum in the 

 position indicated in the figure. In Fig. IJ the initial corallite is 

 seen directed from the center diagonally upward and toward the 

 right. From this initial corallite the others branched oft" at first 

 on the upper side of the corallum, as here figured, and later on 

 the lower side. The base of the corallum in this case was not 

 appressed to a flat surface, but grew freely, so that the corallites 

 on the lower surface of the corallum show semi-cylindrical sur- 

 faces, while at their contacts with each other they show the flat- 

 tened prismatic faces due to crowding. The epithecal layer in this 

 case evidently followed the semi-cylindrical free faces of the indi- 

 vidual corallites, and therefore did not present a flattened surface 

 as in Fig. IH. A considerable collection of specimens showing 

 these lower surfaces was made at one time at the long exposures 

 at stop 11, north of Hulitt station, northeast of Brannon, along 

 the traction road from Lexington to Nicholasville. The Benson 

 limestone here was weathered to clay, overlying, at the base of 

 the cut, the Brannon argillaceous limestone. 



Compared with these Trenton specimens, those from the Mil- 

 lersburg member of the Cynthiana formation, between New For- 

 est station and the overhead bridge two miles south of Millers- 

 burg, show larger coralla but smaller corallites. Corallites 5 mm. 

 in diameter are relatively very large in these Millersburg speci- 

 mens, while their average diameter is nearer 3 mm. They form 

 the variety Columiiaria alreolata-miniina. 



Coliiinnaria, of the alveolota type, makes its first appearance in 

 the upper part of the Black river limestone, at Ottawa and also 



19 



