40 



THE GENUS MONTICULIPORA. 



expect to find traces of the original boundaries between the 

 coralHtes. This state of parts occurs in forms like M. tumida^ 

 Phill., M, Andrezvsii, Nich. (fig. 2, d), M. gracilis, James, M. 

 moniliformis, Nich., and various other allied types. 



Some forms of Monticuliporoids show peculiarities in the 

 structure of the wall slightly different to any of those alluded 

 to above, but the preceding are the most important types with 

 which we have to deal ; and our knowledge on this subject, as 

 derived from tangential sections, may be corroborated, and in 

 some points supplemented, by an examination of longitudinal 

 sections. In these we see the same great apparent differences 

 that have been noted in tangential sections. Thus, in some 



Fig. 3. — A, Long section of the corallites o{ Moilkulipora Ulrkhii, Nich., showing the struc- 

 ture of the wall close to the surface, as well as the "spiniform corallites ; " B, Long sec- 

 tion of two corallites of Montkidipora monilifoniiis, Nich., also close to the surface, 

 showing the thickened wall and the hollow spines ; C, Long section of two corallites of 

 I\Icmticiih'pora petropolitana, Pand. ; D, Long section of the corallites of M. tituUilata, 

 Nich. All the sections are enlarged fifty times. 



forms, like M. petropolitana, Pand., and J/, tuidulata, Nich. 

 (fig- 3. c and d), the walls separating adjoining corallites appear 

 as seemingly structureless, thin, and delicate dark lines, without 



