254 



Cincinnati Society of Natural History. 



The cavity of each tube is surrounded by a secondaiy deposit of dark, 

 concentrically laminated sclerenchyma, while the original wall is repre- 

 sented by apparently structureless (in this section) sclerenchyma, of 

 much lighter shade. The interstitial cells are variable in size and 

 shape, and comparatively much reduced in number, being, as a rule, 

 less numerous than the proper tubes. 



The characters which distinguish C. subplana from all other species 

 of the genus known to me from the Cincinnati Group, are found in its 

 robust growth, the large size of the cells, the conspicuous clusters, and 

 the proportional paucity of the interstitial tubes. 



Formation and locality: Cincinnati Group. Not an uncommon 

 fossil near the tops of the hills south and west of Covington, Ky. The 

 range is limited, being apparently not more than 25 feet. CaUopora s 

 dalei, Ed. & H., Homotrypa curvata, Ulrich, and Heterotrypa sub- 

 pulchella, Nich., are associated species, and appear to have a nearly 

 equally limited range. 



Amplexopora cingulata, n. gen. et sp. (Plate XI., figs. 5-56.) 

 Generic char., ante p. 154. 



Zoarium ramose, consisting of C}dind"ical or subcylindrical branches, 

 which divide dichotomously at irregular intervals, and vary in 

 diameter from three to seven tenths of an inch. The surface is per- 

 fectly smooth, and destitute of monticules. When in the best state of 

 preservation, the cell-apertures are subpolygonal, the walls are 

 moderately thin, and occupied by small granules. In the usual con- 

 dition the cell-apertures are rounded, the walls comparatively thick 

 and smooth. * The surface also shows groups of from seveu to fifteen 

 cells, of a larger size than the average, their diameter varying from 

 -JL-th to -gVth °f an i ncu > while that of the smaller ordinary cells is al- 

 most constantly about -^-th of an inch. 



Tangential sections (PI. XL, figs. 5a and 5&) show that the cells are 

 of one kind (i.e., no interstitial' tubes are present), and that, between 

 the groups of larger cells, they are of a very uniform size. The original 

 potygonal walls can still be readily recognized ; but their internal 

 cavities are more or less rounded by a secondary deposit of dark, con- 

 centrically laminated sclerencli3 T ma, which has a variable thickness in 

 different sections. The original line of demarcation between adjoining- 

 tubes is always more or less distinctly preserved, and is made espe- 

 cially conspicuous by the numerous small spiniform tubuli, which, in 

 this species, are developed only on the line of junction. One is situ- 

 ated at each angle, and one or two more on the line between the angles. 



