American Palo&ozoic Bryozoa. 



129 



of a line running through the center of the tube, so as to partially di- 

 vide the tube into two unequal portions. These are not due to the de- 

 velopment of " spiniform tubuli," as in the preceding instances, but I 

 regard them as the remnants of the peculiar projecting Lip with which 

 the cells in this genus are provided. The feature constitutes a most 

 interesting link between the Ceramoporidai and FistuliporidcB, since it 

 also characterizes the new genus Crepipora, of that family. Hall, in 

 his description of the type species of Callopora (C. elegantula) states 

 that the cells are sometimes provided with radiating septa. For this 

 misapprehension he is not seriously to blame, since without a careful 

 examination of the species, by modern methods, any one might make 

 ;i similar mistake. Perfect specimens of C. elegantula, and other 

 species of the genus, such as C. ramosa, D'Orb., and C. andrewsi,lS[ch., 

 olten have the cell -apertures closed by opercula with a central perfor- 

 ation, from which a number of delicate ridges radiate to the margin of 

 the calices, thus imparting to the cell the appearanee of being really 

 septate. 



VII. Epithecal structures. — The only remaining point of general . 

 structure which deserves a few words of notice, concerns the develop- 

 ment of an epithecal membrane, which, as a rule, is more strongly 

 marked in those types which possess a discoidal zoarium ; and in these 

 the concave or flat under surface is covered by a concentrically 

 wrinkled, thicker or thinner membrane. This epithecal membrane is 

 not unfrequeutly marked also by fine radiating striae, which indicate 

 the bases of the cell-tubes; in other cases (e. </., Prasopora bellula, 

 u. sp.), it is provided with numerous short spinelets. This epitheca 

 has no connection with the opercular structures, often closing the 

 mouths of the cells, as Nicholson seems to think (" Palaeozoic Corals, — 

 Monticulipora," p. 54); nor do I believe that the opercula and epitheca 

 of the Monticuliporoids can be compared to the cortical membrane of 

 certain species of Favosites (e. F. turbinata, Billings, F. clausa 

 and F. tuberosa, Rominger). The membrane of these species of 

 Favosites covers the base and sides of the corallum, so as to leave the 

 corallites of only the upper end open, and it does not seem to indicate 

 anything else, than that the portion of the corallum so covered is 

 dead. On the other hand the epitheca of the Monticuliporidce, and 

 Fistuliporidce, forms a sole or base to the tubes of the zoarium, and is 

 equivalent to the "lame germinale" (D'Orbigny), of so many Bryozoa, 

 and it is really developed in advance of the cells which are to rest upon 

 it. That this is true may be seen more or less readily in all perfect^ 



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