A. E. Verrill — Corals of the Genus Acropora. 229 



the two directives. The outer wall is covered with numerous, very 

 thin costulae. 



The more distal corallites are a little more ascending, but the 

 lower lip is slightly excnrved and expanded, so that the calicles are 

 conspicuous. Some smaller immersed calicles (0.3 mm in diameter) 

 are found between the labiate ones nearly to the tips of the branches. 



The axial corallites are moderately large (2.5 to 3 mm ), with thick 

 walls, and only a little exsert. The axial calicle is small (l mm ), with 

 12 subequal, thin, but not narrow, septa. 



The coenenchyma of the branches is rather dense, with few small 

 pores, and its surface is covered with rather coarse, rough or sharp 

 spinules, not crowded, and mostly arranged in longitudinal series, or 

 often united into irregular costuloe or small tabula?. 



The origin of the type is unknown, but is doubtless Indo-Pacific. 



Acropora effusa (Dana) Ver. See p. 215. 



Madrepora effusa Dana, Zooph., p. 455, 1846. Brook, p. 76 (non Qnelch). 



Plate XXXVI. Figures 16, 16a. Plate XXXVI B. Figures 7, 7a. 



Dana's unique type of this species from Ceylon (coll. Rev. Geo. 

 H. Apthorp) is in the Museum of Yale University. 



It is a regular corymbose clump, with a slightly convex surface, 

 10 by 14 inches (250X350 mm ) across, and 5 inches (125 mm ) high. 

 The upper surface is covered with upright branches 25 to 40 mi " long, 

 arising from a solid basal mass of coenenchyma, covered above with 

 immersed stellate calicles. The base is broadly incrusting, about 

 250 mm across, and free marginally only for a slight distance, except 

 on one side, where the free part is 75 to 100 mm wide. It here forms 

 a nearly solid plate of coalesced branches, with a few submarginal 

 openings, without free branchlets, but covered thickly with exsert, 

 conoidal, verrucose, and tubular corallites, l-3 mm long, with porous, 

 echinulate walls and 6-rayed, stellate calicles, the directives wider. 

 There are few immersed calicles beneath. The coenenchyma of the 

 outside base is very porous. 



The marginal branches are nearly horizontal at base, and coales- 

 cent ; submarginal ones are curved upward distalh r ; those nearer 

 the middle are straight, upright, partly simple and partly forked, or 

 more or less proliferous; they are rather stout and tapered, 10 to 

 1 5 mm thick at base, subacute, with a moderately large, but not swol- 

 len, axial corallite, 2.5-3. 5 mm in diameter, and l-3 mm exsert, with 

 rather thick, openly porous, costulate walls. 



