CORALS FROM MURRAY, COCOS-KEELING, AND FANNING ISLANDS. l8l 



As Brook's figures are not satisfactory, I am publishing five figures, which 

 show the range of variation exhibited by the suite of Fanning Island specimens. 

 Brook has correctly identified the specimen referred by Dana to "Madrepora 

 abrotanoides." 



Dislribution. — Malacca; Fijilslands; Fanninglsland. This evidentlyis awidely 

 distributed species. 



Acropora (Rhabdocyathus) variabilis (Klunzinger). 

 Plate 80, figures 2, 3, 3a, ib, specimen from Cocos-Keeling Islands. 



1879. Madrepora variabilis Klunzinger, Korall. Roth. Meer., pt. 2, p. 17, plate I, fig. 10; plate 2, figs. I, 5; 



plate 5, figs. la, lb; plate 9, fig. 14. 

 1906. Acropora variabilis von Marenzeller, Denksch. k. k. Akad. Wissensch. VVien, vol. 80, p. 23, plate 15, 



figs. 40-44. 



Each of two sets of fragments representing two colonies, obtained by Dr. Wood 

 Jones in Cocos-Keeling Islands, will be described separately: 



Specimen No. I (plate So, fig. 2) : 



Corallum represented by four fragments, which have the following dimensions: 



Dimensions of branches of Acropora variabilis. 



'Measured at the base of the corallites. 



The growth-form, which must be inferred, was apparently cespitose. The main 

 branches subdivide as shown in the figures and there are elongate proliferous corallites or 

 short twigs, ranging m length from 7 to 16 mm., and in basal diameter according to length 

 from 2.5 to 5 mm.; diameter of axial corallites of such twigs about the same as that of the 

 axial corallites of the larger branches. Abnormal axial corallites on twigs near the base 

 of one branch range in diameter from 4 mm. to 4.5 by 6 mm. Axial corallites of the larger 

 branches slightly taper from the base to the aperture. The diameter at the base is given 

 in the table; that at the aperture is about 2.5 mm., or it may be slightly less. The walls 

 are thick, reticulate, become secondarily compact, outer surface granulate, sometimes 

 obscurely but not obviously costulate. Apertures small, from 0.5 to 0.75 mm. in diameter. 

 The primary and usually the secondary septa are distinct, all of which are occasionally 

 subequal. 



The radial corallites are very unequal in size; just below the axial corallites they are small, 

 diameter 1.5 mm., length 2.5 mm., or even smaller, and are appressed tubiform with the 

 outer wall much thicker than the inner. Lower down, within about 8 mm. from the branch 

 tip, the corallites are much larger and attain their normal full size. The proliferous corallites 

 have already been mentioned; besides thesethere are ascending, more or less twisted, tubiform 

 corallites up to 5.5 mm. long and 2.25 by 2.5 mm. in diameter, and appressed tubiform coral- 

 lites, 4 mm. long and 1.75 mm. in diameter, irregularly scattered between the bases of 

 which are subimmersed corallites which may be only 0.75 mm. in diameter. All kinds of 

 radial corallites intergrade; the tubular grade into the proliferous, and the latter become 

 axial corallites. Low down on the branches some radial corallites are appressed veruciform. 

 The walls are thick, early become compact, outer surface closely granulate without definite 

 costules. Apertures small, about 0.75 mm. in diameter, subelliptical, usually more or less 

 eccentric, nearer the inner than the outer margin of the corallite, and often inclined, as the 

 outer wall usually extends somewhat beyond the inner. Frequently the outer wall is some- 

 what tumid just below the aperture and curves up to it. Except in very young corallites 



