CORALS FROM MURRAY, COCOS-KEELING, AND FANNING ISLANDS. 175 



Dana's type of this species, from Fiji Islands, is in the U. S. National Museum, 

 No. 287, and there is a second specimen, also collected by the U. S. Exploring Expe- 

 dition, No. 286. The former is represented by plate 73, figures 2, 2a. Both Dana and 

 Brook fail to mention the presence of immersed or subimmersed corallites between 

 the labellate corallites. In the larger radial corallites 2 cycles of septa may be com- 

 plete, but usually the number of secondaries is variable; the upper directive is the 

 most prominent septum. 



The following is a description of a specimen collected on line I, 800 feet from 

 shore, Murray Island: 



Corallum loosely ramose, with elongate, slowly tapering branches. Branch 91 mm. 

 long has a basal diameter of 11.5 mm.; diameter of terminal corallite, 3.5 mm., the usual 

 diameter of terminal corallites. 



Terminal corallites with thick, porous, longitudinally costulate walls; project up to 

 2 mm.; 2 well-developed cycles of septa, the primaries "almost or actually meeting deep 

 down in the center of the calice, a directive septum sometimes conspicuous. Secondaries 

 extending about half the distance from the wall to the center. 



Radial corallites crowded, of two kinds, labellate and immersed. The labellate coral- 

 lites about 2.5 mm. in diameter, measured from the outer edges of the wall; wall well 

 developed only on the lower semi-circumference of the calice, protuberant about 1.5 mm. 

 at right angles to the intercorallite surface, less prominent near the proximal ends of the 

 branches, often thickened within the calice, but the edge is usually thin, texture porous, 

 outside finely costulate; septa, one complete cycle, directives, especially the upper, con- 

 spicuous, rudimentary secondaries variable in number. The immersed corallites smaller, 

 1 mm. or less in diameter, septa less conspicuous. The two kinds of corallites grade into 

 each other. 



Ccenenchyma reticular, rather porous, with minute echinulations. 



Two specimens from Murray Island are figured (plate 74, figs. 1, 2), in order 

 to show the variation in relative attenuations of the branches and relative frequency 

 of branching. An enlarged view shows the calicular characters. The calices of the 

 Murray Island specimens average larger than those of Dana's type and the wall on 

 the lower side of the calices is more thickened, but the differences seem to me to be 

 due to vegetative variation. 



Stations, Murray Island. — Southeast reef, line I: 



600 feet from shore; depth, 15 inches; bottom sandy; 3 branches. 



800 feet from shore; depth, 11 inches; bottom hard, rocky; 2 specimens. 



1,200 feet from shore; depth, 9 inches; bottom rocky; 3 specimens. 



1,400 feet from shore; depth, 14 inches; bottom hard, rocky; 2 specimens. 



Distribution. — Fiji Islands (Dana's types); Great Barrier Reef. 

 Acropora (Tylopora) digitifera (Dana). 

 Plate 76, figures I, ia, 2, specimens from Murray Island. Also plate 13, figure 7, of Dr. Mayer's article. 



1846. Madrepora digitifera Dana, U. S. Expl. Exped., Zooph., p. 454. 



1893. Madrepora digitifera Brook, Cat. Genus Madrepora, p. 75. 



1902. Acropora digitifera Verrill, Trans. Conn. Acad. Sci., vol. 1 1, p. 228, plate 36, fig. 12; plate 36 B, fig. 3. 



The following is the description of a specimen from Murray Island: 



Corallum with an incrusting base 92 by 100 mm. in diameter, above which a number 

 of branches rise separately; height of colony about 134 mm.; greater horizontal diameter 

 about 207 mm.; lesser horizontal diameter about half as much. The branch terminals 

 reach nearly to a plane. Basal diameter of a branch, about 13 mm.; branches subdivide 

 about 17 mm. above the basal expansion into two or three subordinate branches about 10 

 mm. in diameter at the base and 50 to 60 mm. long. Some proliferous corallites grading into 

 branchlets higher up. Branching more diffuse around the periphery of the colony than 

 near the center. 



