﻿98 MADEEPOEARIA. 



75. Montipora undata. (PI. XXI. fig. 2 ; PI. XXXIII. fig. 9.) 



Description. — Corallum thin, encrusting, the free edges 2'5 to 4'0 mm. thick, at first droop^ 

 ing, but ultimately bending outwards into the horizontal plane ; unsupported by any epitheca. 



Calicles consj^icuous, 0*75 mm. in diameter, the margin not shai-ply circumscribed, rather 

 close to one another in single or double rows in the serpentine valleys between the ccenenchy- 

 matous ridges. For some 2 cm. round the free horizontal edge the calicles are invisible from 

 above, being few in number and pointing outwards from the faces of the ccenenchymatous 

 uprisings. Septal apparatus well developed and symmetrical, the primaries reaching to the 

 half radius circle, the secondaries being about half the size and tliickness. When the apertures 

 are not sharply bounded, the primaries stand up somewhat above the ccenenchymatous 

 reticulum. Individual calicles may rise straight up from the bases of the valleys as thin 

 uniform cylinders 2 mm. in diameter, reaching as high as 5 mm. On the under surface 

 calicles are numerous, and each is surrounded by a delicate ccenenchymatous ring. 



The ccenenchyma is a beautiful, very regular, filamentous reticulum with hardly any 

 differentiation into layers. The streaming layer is, however, just recognisable as such. 

 Eound the edges this foams up into radiating ridges which meet irregillarly or rise into crests. 

 In the central portions of the corallum the ridges are twisted and bent, enclosing serpentine 

 valleys ; here and there they rise into crested knobs or eminences. The floors of the valleys 

 on the more level surfaces seem to be formed of a more open and rapidly growing reticulum 

 than that forming the ridges, which appear as if they were being submerged. The ends of the 

 threads form fine echinulffi over the whole surface. The reticulum of the under surface is also 

 light and open, and only becomes more solid in the older and decaying portions. It may 

 remain smooth or the interstices may hang down either in large cylindrical knobs, or each 

 interstice may bulge down like a gathering drop. 



This coral recalls M. jn^olifera, but the ccenenchymatous elevations are quite different ; 

 they are comparatively thick and open, while in jrrolifera they may be very thin, and so 

 crowded and irregular that the calicles in the deep dark holes and valleys between them can 

 hardly be seen ; the texture of the ccenenchyma is also different. In this last point the type 

 resembles M. spumosa in being an open filamentous reticulum with an echinulate surface. A 

 fragment of a knob, if detached, might easily be classed with M. foveolata, or rather with M. 

 socialis, because the ccenenchymatous ridges form ramparts with a few calicles in the valleys 

 between them, very similar to those in this last named type. 



The serpentine ridges of a central part of the corallum and its drooping edges class it with 

 the last type, if. patinceformis. On the other hand, the vaUeys are much wider and the ridges 

 round the edge are markedly radial. There is, further, no trace of any epitheca, and the under 

 surface is not wrinkled or stony but a light porous reticulum. 



The tall cylindrical calicles are very peculiar, and suggest at first sight the presence of 

 commensal worms, but though small worm-tubes do here and there raise up the ccenenchyma, 

 these cylinders contain true calicles. 



a. Moluccas. Purchased. (Type.) 



