SUB-GENUS HETEROTRYPA. 141 



Monticulipora (Heterotrypa) Dawsoni, Nich. 

 (PI. V. figs, i-zf.) 



Spec. Char. — Corallum having the form of an undulated 

 expansion, of unknown size, and about two Hues in thickness. 

 Surface covered with numerous close-set prominent monti- 

 cules, which are markedly elongated, are placed about a line, 

 or less, apart, and are occupied by corallites which do not 

 differ conspicuously in size from those forming the mass of 

 the corallum. Calices polygonal, thin-walled, about i-goth 

 inch in diameter, without any regular series of small aper- 

 tures, but occasionally exhibiting at their angles of junction 

 a minute circular opening. Normal corallites sub-equal, poly- 

 gonal, at first thin-walled, but becoming slightly thickened 

 as they approach the surface. In the centre of the flattened 

 corallum they are furnished with delicate, wavy, or crimped 

 walls, and are vertical in direction, being in this part of their 

 course entirely free from tabular. They then gradually bend 

 outwards, with a very slight inclination, their walls becoming 

 at the same time thickened, and a moderate number of com- 

 plete horizontal tabulee being developed. 



In addition to the normal corallites (which are mostly of one 

 kind) there are numerous thick-walled, circular tubuli (" spini- 

 form corallites ") developed at the angles of junction of the 

 former, or in the thickness of their walls. 



Obs. — In its general form, mode of growth, and external 

 appearance, this species might perfectly well pass as an ex- 

 ample of either M. vianiumlata, D'Orb., or M. molesta, Nich. 

 The only superficial characters which would lead to its separa- 

 tion are, that the normal calices are not intermingled wath a 

 series of smaller apertures (PI. V. fig. 3/y'), and that the pro- 

 minent monticules are certainly more elongated and com- 

 pressed than is usual in examples of the above (PI. V. fig. 3^). 

 In its internal structure, however, ]\I. Dazusoui is fundamentally 



