142 THE GENUS MONTICULIPORA. 



different from either AI. 7}iainniulata, D'Orb., or M. vwlcsta, 

 Nich., and exhibits a quite peculiar assemblage of characters. 



In tangential sections (PI. V. figs, y, -^d) the corallum is 

 seen to be composed almost wholly of one series of normal 

 corallltes, which are similar In Internal structure, and approxi- 

 mately equal In point of size. Near to the surface, the walls 

 of these corallltes are moderately thickened, though the lines 

 of demarcation between adjoining tubes are not obliterated ; 

 and they are uniformly polygonal in shape. Only an oc- 

 casional interstitial corallite, properly so called. Is present ; 

 but there are numerous minute, circular, thick-walled, darkly- 

 outlined tubuli ("spinlform corallltes"), the apertures of which 

 upon the surface may occasionally be detected (PI. V. fig. 3^^). 

 So far as can be made out, the corallltes of the monticules are 

 in no important respect different from those making up the 

 bulk of the corallum ; though this point Is one difficult to 

 settle absolutely, as a tangential section necessarily cuts the 

 tubes of the monticules at a lower level than it Intersects 

 those of the corallum generally, and therefore exhibits the 

 former at a point where their walls are relatively thinner. 



Vertical sections (PI. V. figs, y and 3/"), taken at right 

 angles to the plane of the frond, show that the precise ar- 

 rangement of the tubes differs from what Is observable In 

 ]\L frondosa, D'Orb., on the one hand, and in M. inaimmilata, 

 D'Orb., and M. vwlesfa, Nich., on the other hand. In M. 

 frondosa, D'Orb., the corallltes of the two sides of the colony 

 spring from the opposite sides of a more or less complete 

 calcareous lamina, which occupies the mesial plane of the 

 colony, and which Is seen In a still more perfect form In M. 

 pavonia, D'Orb. In M. viainimdata, D'Orb., and ]\I. niolcsta, 

 Nich., again, the corallltes of the two halves of the corallum 

 have their origin In an apparently Irregular mesial mass of cell- 

 ular tissue, formed by the bases of the tubes, and there is no 

 sign of any central lamina. In the present species no central 

 lamina exists, but the tubes are quite vertical in the middle 

 line of the frond, each bending outwards, with a very gradual 



