15° 



THE GENUS MONTICULIPORA. 



able, and are slightly thickened at the angles of junction of the 

 corallites. In all, also, the visceral chambers are encroached 



Fig. z'i.—Monticulipora Trcntonensis, Nidi. A, A fragment, of the natural size ; B, Portion 

 of the surface, enlarged eighteen times; c, Part of a tangential section, enlarged eighteen 

 times ; D, Part of the same section, enlarged fifty times, showing the original polygonal 

 walls, and their dense secondary infilling ; E, Part of a longitudinal section, enlarged 

 eighteen times, showing the large and small corallites. From the Trenton Limestone of 

 Peterboro', Ontario. 



upon by a dense secondary deposit of sclerenchyma, of a light 

 colour and laminated texture, so that the cavities of the tubes 

 become oval or rounded. This thickeninof of the tubes is 

 entirely confined to their final or peripheral portions, and long 

 sections (fig. 28, e) show that the tubes in the central region of 

 the corallum are provided with exceedingly thin and delicate 

 walls, and are apparently devoid of tabulse, these latter struc- 

 tures not being developed till the corallites begin to turn out- 

 wards. Transverse and longitudinal sections further show that 

 the species is remarkable for the disproportionate development 

 of the axial region as compared with the circumferential : thus, 

 in a transverse section of a diameter of 30-iooths of an inch 

 about 20-iooths of an inch are taken up by the central axis, the 



