A. E. Yerrill — Corals of the Genus Acro2)ora. 243 



Radial corallites small, prominent, regularly arranged, not crowded, 

 strongly divergent, mostly at angles of GO" to 70°, openly tabular, 

 with the aperture oblique and looking upward, not compressed, nor 

 appressed, inner lip adnate or abortive ; outer lip prominent, nar- 

 rowed distally, concave, slightly or not at all incurved, very thin, 

 fragile, reticulate-porous, regularly costulate, with thin costulae. 

 Calicles relatively large and open ; septa nearly all abortive or rudi- 

 mentar}'; sometimes the directives alone are visible and very narrow. 



Below the middle of the branchlets and on the basal branches 

 are numerous immersed calicles, Q-To to 1™™ in diameter, with rudi- 

 mentary or abortive septa. 



Coenenchyma verj^ openl}- porous and pitted, or vermiculate, and 

 sometimes laniellose at the surface. 



Tahiti, J. D. Dana (coll. U. S. Expl. Exped.). Yale Mus., No. 

 2017. 



This species is closely allied to A. surculosa (tj^pical), and appar- 

 ently to A. corymbosa, as restricted by Brook. Compared with a 

 branch of Dana's type of surculosa from the Fiji Islands (Yale 

 Mus., No. 4181), the latter has much more compact coenenchyma, 

 echinulate in series at the surface ; the radial corallites are shorter 

 Avith a broader, more dimidiate, and flatter outer lip, which is also 

 firmer, much less porous, and more truncate, with more strongly cos- 

 tiilate walls ; the calicles are still more widely open, but have the 

 same sort of rudimentary septa. The rather large, open, immersed 

 calicles are also essentially the same, with rudimentaiy or abortive 

 septa, but they are perhaps a little larger (1-1.20™™). 



Perhaps, with a large series, we might be obliged to reunite the 

 two forms, but with the specimens that I have hitherto seen they 

 seem to be as distinct as many of the recognized species of corymbose 

 Acroporce. Should we unite these species, it would probably be 

 necessary to unite with them, also, 31. corymbosa (Brook), M. cythe- 

 rea Dana, M. symmetrica Brook, and others of the same group, in 

 Avhich the radial and immersed calicles are not stellate, but' have 

 only rudimentary septa. See below under A. symmetrica, jj. 254, 

 and cytherella, p. 253. 



I cannot perceive any appreciable specific differences between 

 this species and A. armata (Brook), as described and figured by 

 Brook (see below, p. 252), and think that they should probably 

 be united. 



