54 MADREPORARIA. 



Form A. florida. 

 Corallum erect, arborescent ; main branches spreading, but their subdivisions are little 

 divergent; branches thick and elongate (25 cm.), scarcely tapering, 3'5 cm. diameter near 

 the base and 3 cm. up to within 3 or 4 cm. of the apex. Rosettes about 1 cm. high and 7 mm. 

 broad, but a few are considerably larger. Axial corallites 2 mm. diameter, sometimes 3 mm. 

 exsert, often a little compressed ; aperture round or slightly oval ; wall firm but not specially 

 thickened. The central corallites of the rosettes have the same dimensions, but the aperture is 

 more or less oblique ; usually the aperture is oval, with a notch in the wall at one or both 

 extremities. Radial corallites of the rosettes spreading, sometimes nariform, more usually 

 half-tubiform or labellate, of variable length up to 2"5 mm. or even more; lip 1'3 mm. broad. 

 Between the rosettes the corallites are nariform, labellate, or immersed, the immersed form 

 increasing in number some distance below the apex. The apex of a branch often shows the 

 formation of the rosettes. At first a few radial corallites become elongate and thicker (4 mm. 

 long and 1"6 mm. thick), with or without one or two radial buds ; those between are labellate 

 or nariform, not over 1 mm. diameter and 2'5 mm. long. Corallum very porous, but becoming 

 dense below; surface dense and echinulate; wall closely striate, the striae more or less 

 echinulate. The star consists of 6 narrow septa in the axial corallites, in the radial ones 

 usually only the directives are noticeable. 



A specimen from Malacca, which I take to represent an earlier condition of this form, 

 differs in the almost complete absence of proliferations worthy of the name " rosette," and in 

 consequence the branches are not so thick, scarcely over 2 cm. The condition of the surface 

 of the whole specimen, which is 32 cm. high, is very similar to that of the apical 3 or 4 cm. 

 of a branch in the more typical form. The stouter corallites are frequently not yet proliferous, 

 and at most bear 3 or 4 short buds. 



Form B, confluens. 



? Madrepora horrida, B.-Smith, Ann. Mag. N. H. 1890, vol. vi. p. 452. 



Corallum forming a frond composed of confluent branches. Base oval, 10"5 by 6 cm.; 

 branches 2 to 3 cm. thick, about 30 cm. long, chiefly in one plane, the subdivisions frequently 

 arched. The upper surface bears a large number of rosettes, from 5 to 15 mm. high, but 

 chiefly about 8 mm. The interval between the rosettes as in form A, excepting that some of 

 the labellate corallites are more elongate. Under surface without rosettes or very prominent 

 corallites ; they are chiefly suberect nariform, short tubular or labellate, with immersed ones 

 scattered between. Corallum extremely porous ; surface reticulate above, becoming firmer 

 below, echinulate; wall finely striate, echinulate. 



A number of other massive specimens in the Collection are probably referable to this 

 variety, and the specimens referred to M. horrida by Bassett-Smith appear to me to be an 

 incrusting form in which the rosettes are not well marked. 



Pacific Ocean : Fiji, Tongatabu, Louisiade Archipelago, Malacca, ? Tizard Bank. 



