16 



most ol' the families in this division; still I have not l)epn ahle to find a cover- 

 ring menihrane in members of the families Calenariidde, Uii)pothoida\ Eunj- 

 stoniellidae and Eulhyridoe, nor in the genera Iiwersinla and AiKirlhrojiora, and I 

 must tlierefore ascribe a Gyninocyst to all these forms. 



The two divisions M(d(icnslc(ia and Cniloslt'tja in reality evenly grade into one 

 another, and there is no doubt that the coilostegous forms have arisen from the 

 malacostegous by the extension of the calcification all over the frontal wall. In 

 some Tluddinoporella species, for instance in Th. e.vpansti (PI. VI b, fig. 5 a), the 

 operculum is surrounded by a completely calcified frame-work, while in most of the 

 species it is connected \vith a small membranous area posteriorly. We find a sim- 

 ilar relation between the species of the extinct genus Rli(i<iasostoma and the 

 species of OnychoceUo, between CcllnUtria and MeinbvankelktiUt and between Micro- 

 pora and such Memhranipora species as Memb. argentea Mac Gill.', in which the 

 membranous area is only represented by an exceedingly small part proximally 

 to the aperture. The close connection between the Membraniporidac and the forms 

 now classed under Micropora, TbalamoporeUa and Sleganoporella, seems never to 

 have been doubted, and therefore older writers, such as Busk, simply refer such 

 sj)ecies to the genus Membranipoiit. Hi neks'" speaks about the relation between 

 the Meinbruniporidae and Microporidae in the following way: »In the most typical 

 forms, such as M. inembraiuicea and .1/. Lacroixi, the entire area of the zore-cium is 

 covered uniformly l)y a membrane, which lies a little below the level of the 

 margin. In others this membrane is calcified to a greater or less extent, and a 

 solid lamina is thus formed, which protects a certain portion of the cell. Bui 

 even in such species, in which this process of calcification is carried furthest, 

 and almost the whole front is hardened into a solid wall, its position within 

 and below the marginal rim at once indicates the mode of growth, and reveals 

 the true Membraniijoridan structure'. That Sniitt has a similar view apjjears from 

 his placing the family Cdlaiiidue, which has a completely calcified, depressed 

 frontal wall, in his suborder Fliistrina. and from the following statement on the 

 family Microporidae'". »Thus in the lull iie\elopnienl of the type, the primary 

 area, in the same manner as in Escharina, disappears, and as this was the most 

 pregnant character of the section Escharina, here, also, we perceive the close 

 proximity of that group, although yet the plain front side and the raised pri- 

 mary margins of Ihe zoa-cia remind us of the Flustrine nature*. 



The answer to the question: whence the Ascophora have originated, is not 

 quite so evident, as we have here a compensation sac, of which organ no trace 



72, p. 179; ■' 22, p. 128; '' lO:!. p 13. 



