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



Acropora cucullata Ver., sp. nov. 



Plate XXXVI D. Figures 8, 8n. Plate XXXVI E. Figure 1. 

 The coral forms a broad, flat-topped, corymbose clump, covered 

 with rather long, moderately stout, upright, dichotomous, and more 

 or less proliferous branches, those toward the margin arching out- 

 ward at the base ; on the under side usually with numerous diver- 

 gent, abortive branchlets. 



The upright branches are mostly 8 to 10™"^ in diameter, and 35 to 

 50"™ or more long, round, or subangular when crowded, little 

 tapered to near the ends, which are rapidly narrowed and a little 

 obtuse. 



Axial corallites moderately thick, about 2.5""", scarcely exsert ; 

 wall thick, porous, rounded, costulate, with many pores between the 

 costulse. 



Radial corallites unequal; the larger normal ones are large, prom- 

 inent, about 2.5-3'"™ long, 2-2.5'"™ broad, divergent at angles of 

 45°-70°, a little compressed, arched-nariform or cucullate, with the 

 wall thickened and convex on the middle of the outer side, and the 

 thick, obtuse outer lip arched and incurved, so as to produce a 

 hooded form on many of the larger corallites. The edge of the lip 

 is thin and lacerate. Between these are many smaller, short, open 

 tubular or subnariform corallites, with thin lacerate lips, and also 

 many that are immersed, with wide, deep calicles, 1-1. lO"""" in 

 diameter. 



The septa are all narrow, and part of them are often rudimentary. 

 In the larger radial corallites the directives are more distinct, but 

 ten other subequal narrow septa are usually visible. In the im- 

 mersed calicles they are mostly obsolete, or nearly so, except the 

 directives, which may meet in the middle, in some cases. But many 

 calicles occur in which all six primary septa are well developed, deep 

 down in the calicle ; others occur with 12 distinct, equal septa, at 

 the edge. 



Many of the upright branches also bear more or less numerous 

 gemmiferous corallites, rather longer and larger than the normal 

 radial ones, about 4°"" long and 2.5™"^ broad. These are also at first 

 cucullate with a thick, arched outer lip, and bear 1-4 small, arched 

 corallites ; some may later become more evenly tubular, like the 

 axial corallites. All the corallites have finely costulate walls. 



Immersed corallites are abundant on the primary branches ; less 

 numerous beneath. The coenenchyma is porous, with numerous, 

 elongated pits, and roughly echinulate. 



