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PAPERS FROM THE DEPARTMENT OF MARINE BIOLOGY. 



15 mm.; of axial corallite, which is damaged, about 3.5 mm. This is a remarkably inter- 

 esting specimen, as on its lower 55 mm. it combines the characters of specimens Nos. 2 

 and 3, and over a small area has the character of forma arabica, while on its distal end it 

 has the characters of the set of specimens next to be described. Some of the corallites near 

 the tip are dimidiate. This specimen will not be more fully described, as the characters of 

 its distal portion will be given under the next specimen. 



Specimens No. 5 (plate 6g,figs. 1, 4, 4a, 5): 



Two of this set of branches have been figured by Dr. Wood Jones. 1 

 Corallum cespitose, attached by a narrow base. Height about 21.5 cm.; horizontal 

 diameter, about 28 cm. 



Dimensions of branches of Acropora pharaonis. 



'Only 1 branchlet, 45 mm. below tip of branch; plate 69, figure 5. 

 'Plate 69, figures 4, 4a. 



The diameter of the aperture of the axial corallites ranges from about 0.9 mm. to a 

 little more than I mm. The walls are thick, about I mm., porous, reticulate, and friable, 

 with plate-like costules on the outside. Two well-developed cycles of septa, the secondaries 

 smaller than the primaries. 



Radial corallites, both protuberant and immersed. The protuberant corallites of two 

 kinds, proliferous and non-proliferous. The proliferous corallites seem especially well 

 developed on the outer sides of branches; their distribution irregular; they are inclined at 

 an angle of about 45 to the surface of the branch; range up to 5.5 mm. long (measured 

 along the lower side); outline very slightly elliptical; diameter up to 3 mm.; 2 cycles of 

 septa, the secondaries the shorter; labellate corallites near the bases of the branches. The 

 non-proliferous, protuberant corallites vary according to the position on the branch or 

 branchlet. On the outer surfaces near the tips they ascend at an angle of about 45 and 

 are up to 3 mm. long (measured along the lower side); 1.5 mm. in diameter, about 1 mm. 

 apart; the outer wall is thick and reticulate, and costulate with intercostular pores; inner 

 wall scarcely developed, short, thin; aperture dimidiate or nariform, subcircular or very 

 slightly compressed; 6 primary septa, the directives prominent, the secondaries rudimentary 

 or entirely inconspicuous. On the inner sides of branches the corallites are shorter, about 

 2 mm.; somewhat smaller, more uniform is size, more evenly distributed, and labellate. 



Coenenchyma costulate and echinulate. 



Regarding this set of pieces, Dr. Wood Jones says: 



"Fragments from different colonies of the most abundant form growing in the barrier 

 pools where there is a moderate degree of broken water at some states of the tide. The 

 colonies grow to a great size and every modification in the degree of raising of the corallites 

 is seen, one colony often supplying branches so different in their minute characters that 

 they differ more widely than do many so-called species. The color is yellowish or brownish 

 in some colonies; the zooid is pale." 



'Proc. Zool. Soc. London for 1907, plate 17, figure 2a. Coral and Atolls, p. 89, figure 24a, 1910. 



