380 BULLETIN 103, UNITED STATES NATIONAL MUSEUM. 



are barel}^ above the common surface, they are chcular, but occa- 

 sionally deformed, and they are shghtly unequal in size. The caUcular 

 fossa is shallow, and the calicular margins are broader than the 

 septa. The columella is small, distinct, lax, and parietal. The 

 costae are well marked, miequal, and rarely touch, and they are 

 thicker than the septa. The costae of the highest order are well 

 developed, and contrast with their rudimentary septa. The septa 

 are delicate, they are thinner midway than elsewhere, and those 

 which reach the columella have a palif onii tooth ; they are not exsert, 

 and are only slightly dentate. The septa are very irregular in their 

 arrangement. There are six systems, and in most of them there 

 are thi'ee cycles with or without a part of a fom'th in one-half of the 

 system, so that there are constantly six septa in a system instead 

 of eight. The endotheca is well developed; and the dissepiments 

 are close, stout, and nearly horizontally parallel. The exotheca is 

 abundant, forming small cells with arched outlmes. Height of 

 corallum 6-8 inches. Diameter of cahces two-tenths inch [ = 5 mm.]." 



Locality. — St. Croix, Trinidad. 



Gregory ^ places Duncan's Heliastraea altissima in the synonymy 

 of Or'bicella acropora (Linnaeus), without giving his reason. He may 

 be right, but tlie calices are large for 0. acropora (here called 0. 

 ammlaris) , and judging from the presence of quaternary septa it is 

 almost certainly distinct. According to Duncan's figm^e every other 

 septum reaches the columella, a septal arrangement which is one of 

 the characteristics of 0. annularis. I did not see the type in London, 

 and think that until it is restudied or additional material has been 

 collected at the type locahty, it will not be possible to reach a positive 

 decision as to the validity of the species. 



G. ORBICELLA CAVERNOSA (Linnaeus). 



Plate 87, figs. 1, Ifl, 16, Ic; plate 88, figs. 1, 2, 3, 3o, 36. 



1766. Madrepom cavernosa Linnaeus, Syst. Nat., ed. 12, vol. 1, p. 1276. 



1901. Orbicella cavernosa Vaughan, Geolog. Reichs. Mus. Leiden Samml., ser. 



2, vol. 2, p. 27 (Synonymy with exceptions noted below). 



1902. Orbicella cavernosa Yerrill, Conn. Acad. Arts and Sci. Trans., vol. 12, p. 



102. 



1915. Orbicella cavernosa Vaughan, Washington Acad. Sci. Joui-n., vol. 5, p. 596. 



1916. Orbicella cavernosa Vaughan, Carnegie Inst. Washington Year Book No. 14, 



p. 227. 



In my first paper referred to in the synonymy I placed Astrasa en- 

 dotliecata, Astraea cylindrico, and Astraea hrevis of Duncan m the 

 synonymy of this species. A. endothecata and A. cylindrica now 

 seem to me to deserve varietal recognition and A. hrevis should be 

 treated as a valid species until additional information concerning it 

 is available. Duncan's Astraea antiguensis, which I doubtfuUy 



1 Geol. Soc. London Quart. Journ., vol. 51, p. 272, 1895. 



