﻿GLABROUS MONTIPOR^. 31 



tliickness from 4' to 5 nimi,.and is formed of a beautiful white, foam-like reticulum, half 

 filamentous and half laminate. Young calicles open here and there- in its face as large round 

 holes, with, their apertures encircled, by an irregular thread-like ring of thin ca3nenchyma. The 

 coral is spongy and light like a piece of pumice stone, reminding one_ of M. spongodes, with 

 which, however, it is impossible to unite it (see p. 37). 



a. Thursday Island, Great Bajirier Eeef, Gbll. Saville-Kent. (Type.) 



14. Montipora exserta. (PI. II. fig. 4; PL XXXI.. fig. 13.) 



Montip&ma exs&>:tay(^^\a\ Chall. Eep., Eeef Corals (1886) p. 174, pi. viii. figs. 5, 5a, 5 J. 

 Montipora scalricwloides, Ortmann, Zool. Jahrb., iii. (Syst.) 1888, p.. 155-;. see also op. cit., iv. (Syst.) 

 1889,, pi 499. 



Description. — Corallum a free horizontal growth (complete- form unknown) attaining a 

 considerable size, 2 mm. thick at growing edge, 8 mm. or more near the centre of attachment. 

 On the decay of the central region, the living layer may extend centripetally, so as to cover 

 over the dead portion (see PI. II.). The epitheca follows the growing edge at varying distances, 

 from 2 • 5 cm. and less. It is thick and wrinkled when newly grown, but appears to get worn 

 off in patches or greatly thinned. 



The polyp cavities minute but conspicuous, O" 75 mm., evenly distributed, about 1 mm. 

 apart, edges of the aperture not very sharply defined, each aperture to the naked eye as if 

 bisected by a sharp white vertical plate, due to the presence of two very prominent septa 

 which stretch across the half radius circle and moreover tend to rise above the surface of the 

 interstitial coenenchyma. Deep down in the cell, these sometimes meet, or again they are 

 sometimes united by a central upgrowth (?. a columella). The distal of these exsert septa, i.e. 

 that nearer to the growing edge, is often higher than, the proximal. These directive septa run 

 at all angles to the growing edge, but very seldom- parallel to it. The four remaining primary 

 septa are very irregularly developed : sometimes one or two are pronounced, at others they 

 are hardly distinguishable from those of the; secondary cycle, aL. alike being thin and feebly 

 developed. The poliyp cavity is deep. 



Coenenchyma. In section,, there is the typical streaming layer running straight out to 

 the growing edge. It consists of broad, thick bands and is very massive. Here and there, 

 where parasites have bored through the epitheca, sheets of solid matter form within this layer. 

 Prom under it a thin layer of finer threads bends down to form the under surface, grown over 

 in time by the epithecai Above it, a well developed layer of reticulum thickens the corallum 

 and has its vertical elements only faintly suggestive of trabeculse. It is more of a lattice-like 

 reticulum of coarse texture and. small meshes. The level surfaces of the interstices consist 

 of irregular jagged flakes. 



There is but one specimen), which appears as if it were a sector of aiflat plate which may 

 have been some 40 cm. in diameter. The portion, of the centra of the-, plate which, came away 



