8 Dr. G. Liudstrom on the Apiiities 



though not always formed at these points. On the contrary, 

 the bare patches, or " maculas " of autliors (the thin, smooth, 

 calcareous membranes which have completely covered the 

 oriHces of several cells), are also sometimes elevated so as to 

 form " montiouli." This is the case, at least, with M. ostio- 

 latoj and with Russian specimens of M. jyetrojjolitana, where 

 monticules formed by the large cells are almost wholly covered 

 by a membrane, which forms a macula. ]\Iacula3 are seen only 

 where there are monticuli,or groupsof largecells. Theexcellent 

 figures of some Silurian Monticulijyoro' in the works of Milne- 

 Edwards (see Pol. Foss. des Terr. Pal. pi. xix.) show the same 

 featm*e. This, however, is not peculiar to the Palaeozoic Bry- 

 ozoa ; since J. Haime has described Bryozoa of the genera 

 Heteropora and Ncuropcrra^ from tlie Jurassic formations of 

 England and France, as not only having " macula? " hiding 

 the cells beneath them but also montiouli (" mamelons ") and 

 tabulae, Just as in Monticulipora (" Bryozoaires Foss. de la 

 Form. Jurass.," M^m. Soc.G^ol. de France, 2^ ser. t. v. part 1, 

 p. 207). The maculae in question may be identical with the 

 smooth patches which are so prominent in the Cretaceous 

 Bryozoan family Clusidte ; and it may be doubted whether 

 this phenomenon, which was periodical and not constant, is 

 not of the same nature as the calcareous membrane which is 

 so often seen to close the orifices of the cells in recent Bry- 

 ozoa (e. g. Betepora intricaria^ Fr. Smitt). It occurs also in 

 single cells of some species of CJnetetes and Gallopora^ where 

 it is seen in all stages, from a mere commencement round the 

 wall of the zooecium to its complete form. Rominger regards 

 til is covering as an operculum, which it cannot be, the forma- 

 tion of such a cover necessarily proceeding in a way quite 

 opposite to what obtains in the Bryozoa just mentioned. 

 Moreover there seems to be no instance of the genuine oper- 

 cula of certain Bryozoa having ever been preserved in a fossil 

 state, as these structures are of a corneous nature. It is re- 

 markable that such unquestionable corals as the Favositidae 

 often have had their calices closed in a somewhat similar way. 

 In these the orifices of single calices are closed by a thin, oper- 

 culoid, calcareous membrane, formed, as in the Bryozoa, by 

 successive strata, which grow concentrically from the wall 

 towards the centre, where they are often left incomplete and 

 not filled up. There are also species in which several adjoin- 

 ing calices are covered in a similar manner. In the Favositid^ 

 these covering membranes are clearly of an epithecal nature, 

 being a direct continuation of the epitheca, which spreads 

 successively over the calicles, as may be seen nowhere so 

 clearly as m the strange Devonian Favosites turbinata, Bill. 



