A. E. Yerrill — Corals of the Genus Acropora. 255 



The normal distal radial corallites are ascendiiio: and loosely- 

 imbricated distally, ronnd, dimidiate-tnbnlar, with an elongated^ 

 straight, slightly incnrved, or a little flaring, hollow lower lip, which 

 is sometimes very slightly thickened ; its edge is obtuse and dentic- 

 ulate ; wall strongly costulate with rows of pores in the grooves ; 

 inner lip thin, mostly adnate. 



The calicles are rather large, about 1"'"' in diameter, round or 

 nearly so, and look upward and slightly outward. 



Lower down, the lower lip rapidly becomes shorter and mostly 

 disappears on the bases of the branchlets and on the larger branches, 

 where open immersed calicles are numerous and conspicuous ; they 

 are usually at least 1""" in diameter. 



Septa in all the radial calicles are nearly all abortive or rudimen- 

 tary ; often two very narrow directives are alone present ; in other 

 cases 4 or more additional rudimentary ones can be seen with a lens, 

 especially in the immersed calicles. 



Coenenchyma is roughly and irregularly reticulately pitted and 

 vermiculate, and with rough echinulations in series. 



Zanzibar. No. 79. Exchange, from Peabody Inst., Salem. 

 Branches of other specimens, with longer branchlets, from Mozam- 

 bique, are in the collection. 



Although this specimen appears to be identical with A. symmetrica, 

 I have described it pretty fully, to show its probable identity with 

 A. surciilosa Dana. 



I have compared it directly with Dana's original types of the 

 latter in the Yale Museum, and can find no tangible differences 

 between it and No. 4178, from Tahiti, and others, in the details of 

 the corallites. The walls, lips, calicles, and septa are identical, 

 except that the calicles of the Tahiti specimen may be in part a 

 trifle smaller, and the branchlets that I have at hand are also a little 

 smaller, but they do not differ so much as do those from contiguous 

 parts of our specimen. 



The somewhat greater length of the upright branches of the 

 upper side and the abundance of imperfect proliferous branchlets 

 on the lower side, are the only noticeable differences. 



These are both veiy variable characters in coiymbose corals of 

 this group. Therefore I believe that the two forms should be 

 united. 



The above description may be considered as essentially a descrip- 

 tion of A. surculosa, as to the details of the corallites, calicles, and 

 coenenchyma. 



