68 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



greater diameter, 6.5 mm., lesser, 6.5 mm. ; upper end, greater diameter, 7 mm., 

 lesser, 5.5 mm. 



The upper edge of the wall is rather thin, but below it is very much thickened — 

 there is so much internal deposit that practically the whole of the internal struc- 

 tures are obliterated. An incomplete, pellicular epitheca extends to within 6 mm. 

 of the calicular edge. The wall is costate, the costae are perforated, low, sub- 

 acute, and granulated on the edge, with narrow, perforated intercostal furrows. 

 Every fourth costa is slightly larger than those intervening. 



The septa are in four complete cycles, the primaries and secondaries are equal 

 and extend directly to the columella, the tertiaries are included between the dis- 

 tally diverging quaternaries, which fuse before tlie tertiaries and are connected by 

 a plate with the columella. The primaries, secondaries, and quaternaries are thick, 

 the tertiaries are decidedly thinner. The septal margins are only slightly exsert, 

 arched above, the inner margin falling perpendicularly to the periphery of the 

 columella. The septal faces are densely beset with obtuse or truncated granu- 

 lations, which, especially near the septal margins, show serial arrangement. 



The columella is large and prominent, greater diameter, 3.5 mm., half the greater 

 diameter of the calice ; lesser diameter, about 2 mm., one-third the lesser diameter 

 of the calice. Its upper surface is slightly domed, rising above the level of the 

 septal fusion to its sides. It is composed of thin curled flakes that are united one 

 to another by synapticula. 



The calicular fossa is shallow, about 1.6 mm. its maximum depth. 



Locality : — Station 4643, southeast of the Galapagos Islands, about 4^ miles 

 west by south from the west end of Hood Island ; depth, 100 fms. ; bottom, 

 broken shells and Globigerina; temperature of the bottom, 67.2°. 



Remarks : — This species is so peculiar that I do not know of any other one 

 with which to compare it. It presents only generic similarity to B. elegans 

 Verrill, from the Pacific coast of the United States, and it is not closely related 

 to any of the Hawaiian species of Balanophyllia known to me. Probably B. 

 (Thecopsammid) gemma Moseley is the most similar, but B, galapagensis is much 

 more elongate, and differs in the details of the septal arrangement. 



ACROPORA Oken. 



Four specimens belonging to this genus were obtained from Manga 

 Reva. Oue specimen is incrusted with nullipores and is not in condition 

 for positive specific determination, it, however, is closely related to Aci'o- 

 pora {Tylostoma) humilis (Dana) and may belong to that species. 



It is with a feeling of positive regret that I describe two supposedly 

 new species of this genus, but I have been utterly unable to refer them 

 to any described species. 



Acropora mangarevensis, sp. nov. 



Plate 6, Fig. 3 ; Plate 8, Fig. 1. 



Corallum rising from a stout pedicel, 61 by 35 mm. in diameter, irregularly vasi- 

 form, fusion of the branches imperfect near the periphery. Height of specimen, 

 20 cm. ; diameter of vase, 24.5 cm. ; depth of vase, 7.7 cm. 



