164 



Cincinnati Society of Natural History. 



cumscribed and peculiarly marked lateral margins of the fronds of 

 this Polyzoan type; and, what is more important, it is without the 

 peculiarly striated central lamina of the Ptilodictyce. It is true that 

 the bases of the corallites in M. pavonia, D'Orb., are so united with 

 one another as to give rise to an irregular calcareous membrane, which 

 separates the two halves of the corallum; but none of the specimens 

 that I have seen exhibit any tendency to split along the line of this 

 membrane, nor can the corallites be forcibly removed from one side of 

 it, exposing the median lamina as a definite structure. In both these 

 respects the Ptilodictyce would show quite different phenomena." The 

 first character — i. e., the nonporiferous margin which Dr. Nicholson 

 erroneously regards as lacking in P. pavonia — is, of course, not devel- 

 oped along the growing margin of the fronds, but in all specimens 

 preserving the " articulating process," the non poriferous margin may 

 be traced along the edges of the lower portion of the frond. The non- 

 poriferous margin in P. pavonia (Plate VII., fig. 3a), is precisely like 

 that of either P. falciformis or P. maculata. Judging from the 

 above quotation, it would appear that Dr. Nicholson has entirely mis- 

 conceived the character of the median laminae of the Ptilodictyonidai. 

 If I understand him correctly, he believes that the axis is constituted 

 by a definite structure from which the two laj^ers of cells may be 

 striped. This impression is manifestly erroneous, nor do I know of a 

 single double-leaved Bryozoan in which such a structure may be 

 demonstrated. In Ptilodictya the facts are, simply, that we have two 

 layers of cells which are grown together back to back by the adhesion 

 of the epithecal laminae of each layer. This fact may be readily 

 demonstrated either in thin sections or fractures. In both tests the 

 characters presented by P. pavonia. are precisely like those observed 

 in other species of the genus. On plate VII., figs. 3 and 3a, are repre- 

 sented two specimens of P. pavonia, both of which preserve a portion 

 of the frond and the articulating process. The importance of the fact 

 that this species possesses ajointed zoarium can not be over-estimated, 

 since it completes the chain of evidence that establishes the near 

 relationship of P. pavonia to some of the more typical species of the 

 genus. 



Formation and locality: P. maculata is not an uncommon fossil in 

 strata about 300 feet above low- water mark in the Ohio river, at Cin- 

 cinnati, Ohio, Covington, Kentucky, and other localities. 



Ptilodictya ramosa, n. sp. (Plate VII., figs. 5, 5a.) 

 Zoarium ramose, branching dichotomously about three times, at in- 



