CLOSUEE OF THE CTCLOSTOMATOUS BETOZOA. 401 



Beticulipora nuomnulitorum, d'Orb., but wMcli I afterwards 

 named B. dorsalis, from Naples (" Bry. of Naples," Ann. & Mag. 

 Nat. Hist. 1879, iii. p. 278, pi. xxiii. fig. 5), and figured a similar 

 cover witli a projecting tubule ; and since then Mr. Hincks bas 

 figured tbe same thing in Diastopora sarniensis {' Brit. Polyzoa,' 

 p. 463, pi. Ixvi. figs. 7-9), and refers to their having been consi- 

 dered subservient to reproduction ; but none of us fully appre- 

 ciated that this closure is only a modification of what occurs in 

 the zooecial tubes of all Cyclostomata. 



Mr. J. Young, in the ' Geological Magazine ' (new series, vol. i.), 

 called attention to Polypora, Carboniferous Bryozoa having the 

 aperture nearly closed by a thin calcareous cover with a minute 

 opening in the centre. These closures, which are nearly terminal, 

 have been thought to be homologous with the radial denticles 

 of Glauconome stellipora ; and the existence of this calcareous 

 cover in Palseozoic Bryozoa has attracted considerable attention. 

 In "Eemarks on some Fenestellidse," Manch. Geol. Soc. 1878, 1 

 mentioned, as bearing upon the last point, that " in the Cyclo- 

 stomata the cells are often after a time closed by a diaphragm, in 

 most cases some little distance down the tube;" and further 

 examination enables me now to state that the position and the 

 character of this diaphragm may be employed as a useful specific 

 character. 



The most usual position for the calcareous plate which closes 

 the tube would seem to be about the point where the zooecial 

 tube rises free from the zoarium. This can very well be seen in 

 what I call Entalopliora rugosa, d'Orb., from Naples ; and in 

 successful sections we cut through this plate and see it as 

 figured (PL XVII. fig. 3). In Idmonea the closure is usually 

 in about the same position as in M. rugosa, while in Crista it is 

 terminal ; and we have seen that in Mesenteripora and some Dia- 

 stoporcB it is terminal with a projecting tubule, and in several 

 Palseozoic fossils it is almost terminal. 



Besides the position, we must also notice the character of this 

 plate ; for sometimes it has one opening, in other species there 

 are a number of openings, as figured by Hincks in Diastopora 

 patina, or there may be only very minute perforations, and it is 

 apparently sometimes quite closed. 



Mr. E. D. Longe published a paper in the * G-eological Maga- 

 zine ' (Jan. 1881), " On the Oolitic Polyzoa," in which he main- 

 tains that certain closures are the equivalents of the opercula of 



