CORALS FROM MURRAY, COCOS-KEELING, AND FANNING ISLANDS. 171 



in size. On the same specimen of A. pharaonis there are areas in which the calicular 

 margins are protuberant and other areas in which the corallite walls do not project 

 beyond the ccenenchymal surface. Plate 70, figure 1, represents a colony in which 

 the calices are only slightly protuberant. This form of colony is represented by or 

 intergrades with specimen No. 3, described on page 167. On one side of the latter 

 specimen a large part of surface has calices similar to those represented by plate 

 70, figures 2 and za. 



Dr. Wood Jones says regarding the specimen illustrated by plate 70, figures 



2 and za: 



"Fragments of a colony showing the extreme degree of flattening of the corallites due 

 to the absence of any sediment in the water of its habitat. Whole colonies of this facies 

 are found, in which the corallites are flattened and the growths are characteristic. The 

 ends of the branches are rounded and apical zooid is not marked. Occasionally branches 

 of this facies are found on colonies of other facies, and in all old colonies the older branches 

 tend to assume this form unless sediment is abundant." 



Von Marenzeller considers forma arabica as "Widerstandsformen des bewegten 

 seichteren Wassers" (see quotation on page 170). 



Acropora (Polystachis) corymbosa (Lamarck). 

 Plate 67, figure 1, specimen from Cocos-Keeling Island. 



1893. Madrepora corymbosa Brook, Cat. Genus Madrepora, p. 97. 



1906. Acropora corymbosa von Marenzeller, Denksch. k. k. Akad. Wiss. Wien, vol. 80, p. 32, plate I; 



plate 2, figs. 1-8; plate 3, figs. la-Sa, 9. 

 1910. Madrepora F. Wood Jones, Coral and Atolls, plate 3, opposite p. 76. 



The following is a description of a specimen of this species from Cocos-Keehng 

 Islands: 



Corallum fan-shaped, with branchlets projecting upward on the upper surface except 

 near and around the margin. Branchlets up to about 40 mm. long, simple or bifurcating, 

 some trifurcating, radially compressed. Diameter of base of a simple branchlet 5 mm.; 

 by fusion of their bases plates 22 mm. wide may be formed, thickness of such a plate 5 mm. 



Axial corallites, 1.5 mm. to 2 mm. in diameter; project about 1.5 mm.; wall porous, 

 reticulate, radial costules well developed, thickness about one-third the diameter of the 

 corallites; 6 primary septa well developed, the directives usually meet in the axis; rudi- 

 mentary secondaries frequently but not persistently distinguishable. 



Radial corallites ascending, appressed, tubo-labellate; near the tips of the branchlets 

 the outer margin is much taller than the inner and sometimes curves upward; walls thin, 

 delicate, perforate, costulate. Farther down on the branchlets, the wall on the outside 

 may not project higher than on the inside. Diameter, about 1.25 mm.; length (on outside), 

 up to 3 mm. Aperture elliptical. Six primary septa usually distinct, directives conspic- 

 uous; secondaries rudimentary, obscure, or absent. The corallites become less prominent 

 toward the bases of the branchlets, and on the main branches are subimmersed or immersed. 



Ccenenchyma perforate, costulate, and echinulate. On the branchlets it is a very 

 porous lax reticulum. 



Habitat, etc., Cocos-Keeling Islands.— Dr. F. Wood Jones furnishes the following 

 notes: 



' 'Fragments of a particularly fine colony, the only one of precisely this kind found. It 

 formed the summit of a composite mass in the inlet between Pulu Pasir and Pulu Tikus. 

 Many of the great fan-shaped branches measured 5 to 6 feet across. The fan-shape was well 

 developed, but the plate formation was not so complete as in colonies seen on the barrier 

 reef. Only at its base was there any marked anastomosis of branches. The color while 

 alive was brown; the distal ends of the branches were white or pale yellow." 



Dr. Fred Baker has sent to the U. S. National Museum a specimen which he 

 collected at Fanning Island and which I am referring to this species. It is a fan- 

 shaped frond with branches projecting upward on its upper surface. Von Maren- 



