126 Cincinnati Society of Natural History. 



usually number three or four in each tube. Transverse sections show 

 the tubes in the center of the branch, to be polygonal, without minute 

 intercellular tubuli, and with A'ery thin walls. 



From an external examination, when the pseudo-septa are not visible, 

 it is not an easy matter to distinguish specimens of this species from 

 certain varieties of Chmtetes {3Ionticulipora) pidchellus ; but when 

 worn there is no difficulty, as the septa, when viewed through a hand 

 lens, give a peculiar and characteristic appearance to the specimens. 

 Of course tangential sections will immediately demonstrate their dis- 

 tinctness. The ramose growth of the species will distinguish it from 

 the other species of Atactopora. 



Formation and locality: specimens of this species are not uncom- 

 mon on the hills back of Covington and Cincinnati, at an horizon of 

 about three hundred feet above low water mark in the Ohio river. 



Collectors: J. Ralston Skinner, E. 0. Ulrich. 



Genus Stellipora (Hall.) 

 Stellipora eimitaris, n. sp. (Plate XII., figs. 8, 8a, 8&, 8c.) 



[Ety. — Liinitari.9, on the border.] 



Grows in cylindrical or sub-c^dindrical, sometimes hollow branches, 

 the diameter of which varies from three to five lines; or in small lo- 

 bate or sub-palmate masses. Branches in the ramose examples divid- 

 ing dichotomously at varying distances, irregularly thickened and no- 

 dulated. Surface with the tube-mouths on all sides, the tubes cylin- 

 drical and radiating in all directions from an imaginar^^ central axis. 

 Scattered, generally over the entire surface, are numerous stellate 

 spaces, each of which has a diameter of a line or a little more, some- 

 times considerably depressed, but usually on a level with the surround- 

 ing surface; the number of the ra3^s radiating from the body of the star 

 varies from five to eight; these frequently bifurcate once or twice, and 

 unite with those emanating from the adjacent stars, thus producing a 

 sort of net-work. The stars are usually regular in outline, sometimes 

 elongated, and arranged in rather irregular transverse or oblique rows, 

 three stars generall}^ occupying a space of three and a half lines; it is 

 however not very rare to find specimens with a portion of the surface 

 destitute of the stellate spaces. The central area and the rays of the 

 stars are composed of aggregations of very minute sub-angular tubuli. 

 but appear to be solid, unless examined with a sufficiently high mag- 

 nifying power. The surface between the stellate macula? is covered 

 with small circular calices, the margins of which, in protected parts, 



