140 



Cincinnati Society of Natural History. 



imates closely to both the Fistuliporidoi and Monticuliporidce. In 

 Stictopora, Stictoporella and species of Pachydictya, the zoarium has 

 a definite form, the lateral growth of the fronds being limited by the 

 thickening at the edges of the median epithecal laminae, and the 

 formation of a non-poriferons margin. In the first genus the cells are 

 of one kind only; in the second, beside the true cells, interstitial pits 

 are developed; and in the third, a greater or less number of interstitial 

 tubes are present, which at maturity are covered by an interstitial 

 membrane. In Phyllodictya the differentiation is carried still further, 

 and we have a flabellate or irregular zoarium, with the cell-structure 

 like that of Pachydictya, excepting that in the perfect state the 

 margin of the cell-apertures is prominent on one side so as to form a 

 small "lip." Diaphragms are developed in both kinds of tubes in 

 Pachydictya and Phyllodictya, and occasionally small spiniform 

 tubuli are present. The zoarium now before us has, beside, a small 

 number of spiniform tubuli, two sets of tubes, both of which are 

 provided with diaphragms, with those in the interstitial tubes more 

 numerous than those which cross the true tubes. The tubular struc- 

 ture is, therefore, like that of many Monticuliporoids ; and the closing 

 of the interstitial cells by a thick membrane, points to a decided 

 affinity with the Pis tulip or idee. And this relationship is nearly 

 assured by the remarkable genus Cystodictya, in which not only an 

 interstitial membrane is developed, but the interstitial space, as is 

 shown by vertical sections, is occupied by a vesicular tissue precisely 

 like that of the Pis tulip or idee. A similar interstitial membrane is 

 developed in Ceramoporella, Ulrich, and many of the Mesozoic Cy- 

 clostomatous Bryozoa. The structure of the cell-tubes of such species 

 of Ptilodycta, as P. pavonia, D'Orb., P. falciformis, Nich., P. (He- 

 terodictya) gigantea, Nich., and P. maculata, Ulrich, is not irrecon- 

 cilably different from that of the Monotrypellaz; and distinct "monti- 

 cules" are present in P. pavonia and P. maculata, while "maculae'' 

 are characteristic of Phyllodictya, Pachydictya and species of Phcen- 

 opora. 



Despite the arguments used by Dr. Nicholson (" Gen. Monticulipora," 

 p. 73, et seq.) to demonstrate his view of the relations between Heter- 

 opora and the Monticuliporidce., I shall attempt to show that there 

 does exist decided and true affinity between the Heteroporce and 

 certain genera of the Monticuliporidoe. The species of Batostomella, 

 Ulrich, ranging in time from the Trenton Group to the Carboniferous, 

 are the first which will be specially considered in this question. 



