188 Prof. P. M. Duncan on the Hard Structures of 



XXV.— Ow the Hard Structures of some /S^eaes o/" Madrepora. 

 Bj Prof. P. Maetin Duncan, F.R.S.; V.P.L.S.,&c. 



The object of this examination of three species of the genus 

 Madrepora is to afford information regarding the nature of the 

 growth of the colony, of tlie method of the gemmation, and 

 of the development of the septa. The communication also 

 refers to the porosity of the forms, as well as to their different 

 endothecal structures. 



It was found to be advisable to stain the specimens with 

 carmine, so as to obviate the glare of light. 



Tavo of the three species are known ; but as only portions 

 of the colony of the first one which will be noticed are in 

 iny possession, it is necessary to give a brief description of it. 

 First species : — 

 Colony large, branching, with long, slender, pointed branch- 

 lets, which have ramuscnles on their flanks of from 0*5 in. 

 to 1*5 in. in length. Colony very proliferous. Apical coral- 

 lites sometimes 5 millim. in length, circular at the margin, 

 with a wide calice, showing one cycle of well-developed septa 

 and sometimes a second cycle. 



The apical corallite has much porous mural structure around 

 the calice. The secondary corallites exist all around the 

 axial ones, are numerous, long (i3 millim.), tubuliform, out- 

 wardly curving, very porous, costulate, and faintly nariform. 

 Immersed calices are rare. The costaj exist, but are confused 

 upon the surfaces at the bases of the secondary corallites, where 

 there is a very decided spinulation. Gemmation is frequent, 

 and is noticed on the apical and the secondary corallites. 

 The locality is Madagascar. 



It is evident, from the general appearance of the specimens, 

 that they were very vigorous and rapid growers, the hard 

 parts being perfectly well developed, but thin, and, except in 

 old parts, not thickened with an extra deposition of carbonate 

 of lime. The number of young buds is great, and the porous 

 tissue around the older corallites is delicate and well seen. 



The surface of the corallites is costulate and echinulate,- 

 and the costai are very regularly disposed, in rows, down the 

 outside of the corallites, from the calicular margin to the 

 general surface, where they become confused. They are sub- 

 equal, thin, lamellar, and plain at the free edge in some parts, 

 but exceedingly spinulose in others. They project regularly 

 and equally from the wall of the corallites, and are imper- 

 forate. The intercostal spaces are broader than the cost^ ; 

 but these last project more than the breadth of the interspaces. 



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