CORALS FROM MURRAY, COCOS-KEELING, AND FANNING ISLANDS. 179 



The last clause shows that Brook was aware of the close relation of some 

 of the Great Barrier Reef specimens to his hispida. A number of the incipient 

 branchlets of the Murray Island specimens have only a single axial corallite, indi- 

 cating close relationship to the subgenus Tylopora. 



The specimens (see plate 79, fig. 1) obtained by Dr. Wood Jones in the Cocos- 

 Keeling Islands differ from the type of A. labrosa in having radial corallites which 

 average longer, up to 5 mm. (their length in the type 2 to 3.5 mm.). 



Stations, Murray Island. — Line I, southeast reef: 



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

 1,000 feet from shore; depth 17 inches; bottom rocky. 

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

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

 1,600 feet from shore; depth 10 inches; bottom hard, rocky. 

 Lithothamnion ridge, 1,725 to 1,775 feet from shore (an incrusting lamina). 



6 miles east-northeast^ from Murray Island, inner side of a reef patch of the outer barrier reef, south 

 of Cumberland's Entrance; depth about 4 feet at lowest tide; bottom rocky. 



The only specimen which suggests variation in response to habitat is the one 

 from the Lithothamnion ridge. 



Habitat and color, Cocos-Keeling Islands. — Dr. F. Wood Jones states : 



"From the lagoon at the eastern side of Pulu Tikus, water 1 fathom deep. The colony 

 the only one of its kind found, was luxuriant, made up of large, flat branches over 2 feet in 

 height. Colony pale buff yellow in color; the zooids pale." 



Distribution— The following localities are represented in the U. S. National 

 Museum: Corregidor Light, Manila Bay, Albatross, 1908; southern Philippines, 

 J. B. Steere; Sulu Sea (Dana's type of A. labrosa). Brook records specimens from 

 New Guinea, Solomon Islands, China Sea (Tizard Bank, 5 fathoms), and Diego 

 Garcia. Bedot reports it, as A. hispida, from Amboina. 



Acropora (Isopora) plicata (Brook) 

 Plate 80, figures I, la, lb, from Murray Island. 

 1893. Madrepora plicata Brook, Cat. Genus Madrepora, p. 134, plate 9, fig. D. 



Brook's description of this species is excellent and fits two specimens collected 

 by Dr. Mayer at Murray Island. The striking specific characters are the rela- 

 tively short (2.5 to 8 cm. long) and thick (average about 1 cm.) plate-like branches, 

 along the surfaces of which are longitudinal ridges, bearing rosettes of corallites, 

 composed of a central larger surrounded by smaller corallites; and the tubular 

 radial corallites, which range from 1 to 2 mm. in diameter, are appressed near 

 the branch ends and spreading lower down, the walls are thin, and the apertures 

 relatively large. Two cycles of septa are usually distinct, but small, except the 

 directives, which are wide; four of the primaries are only slightly larger than the 

 secondaries. 



This species groups with A. securis (Dana), type No. 304, U. S. National 

 Museum, and A. cuneata (Dana), type No. 334, U. S. National Museum, as Brook 

 clearly stated. All three have tubular corallites and longitudinal ridges, with 

 rosettes of corallites, on the sides of the plates. The corallites in both A. securis 

 and A. cuneata are more spreading than in A. plicata. 



A. securis has corallites of nearly the same diameter as A. plicata, but they 

 average decidedly more prominent, a height of 3 mm. being common. In addition 

 to the differential characters mentioned, the plates of A. securis are taller, thinner, 

 and more squarely truncate on top than are those of A. plicata. 



In A. cuneata the radial corallites near the plate summits have about the 

 same diameter (about 2 mm.) as in A. plicata, but lower down on the sides of the 



