﻿TUBEECULATE MONTIPORiE. 127 



104. Montipora scutata. (PI. XXII. fig. 2 ; PI. XXXIII. fig. 20.) 



Description. — Corallum thin, horizontal, semicircular, dish-shaped, with gradually rising 

 edges. Growing edge 2 mm. tliick, 5 to 6 mm. in the thickest central region, which is, how- 

 ever, thickened by successive thin layers flowing back from the edge over corroded previous 

 growths which serve to attach the stock. An epitheca appears here and there under the 

 creeping edge, and is well developed under those portions of new growth which happen to arch 

 freely over the old. In sections no line of division can be made out between the successive 

 layers except where they grow free of one another. In the under surface the epitheca is 

 developed only in patches, the greater portion of the whole being free. 



The caUcles are small, • 75 mm., and star-like, deep and conspicuous ; portions of two 

 cycles of very thin septa, the primaries being of unequal lengths, one, however, generally 

 reaching beyond the half radius circle. The periphery of the aperture seldom clearly seen on 

 account of the crowd of tubercles. On the under surface the calicles are crowded, more 

 regularly star-like, with thick, stout septa of irregular length, and forming portions of two 

 cycles ; the apertures, which average about • 5 mm. across, are surrounded by solid rings of 

 coenenchyma which are very conspicuous, • 75 mm. in diameter, and are all slightly prominent, 

 here and there standing nearly a millimetre above the surface. 



The coenenchyma consists in section chiefly of the reticular streaming layer ; the upper 

 thickening layer is thin, the trabecular sunken portions of the tubercles being very little 

 developed. These latter are flat plates expanding a little as they rise, and not at all unlike 

 the scales on the wings of butterflies. These plates, though larger near calicles than else- 

 where, are not arranged radially round the caliele apertures, but very nearly parallel to one 

 another. While the direction in which the scale-like tubercles stand is by no means the 

 same over the whole corallum, there is a decided tendency for them over deflnite areas to face 

 the same way. They are largest and most crowded in the older and deeper central portion 

 of the dish-like corallum ; towards the growing edge they occur more in groups roimd the 

 calicles. 



There is only one undoubted specimen of this coral, showing the peculiar specialisation of 

 the tubercles evenly developed over the whole surface. It shows a remarkable division line on 

 both upper and lower surface (see PI. XXII.). On the upper it is a thin, reticular, creeping 

 edge, with here and there an epithecal film visible, while on the under side there is a white 

 film following the same line as does the creeping edge on the upper side. That this coral is 

 regenerated by successive layers, examination of the older central region conclusively proves, 

 and yet the two halves of the coral on the two sides of the line just described do not seem 

 to differ in thickness. This is not easy to understand, but probably the one half of the 

 coral was neginning to die down, and the other more vigorous half was threatening to 

 grow over it. More puzzling still is the fact that on the under surface the edge of the 

 vigorous region is covered by a thick film, which is quite flush with the old coral and does 

 not spread over it. 



