CORALS FROM MURRAY, COCOS-KEELING, AND FANNING ISLANDS. 20I 



The following is a brief description of the Murray Island specimens: 



Corallum rises above an incrusting base and forms gibbosities, which are short, low, 

 rounded lobes and flat-topped ridges; rather more iobate than in P. rnayeri. 



Calices about as in P. mayeri. 



Wall membranous, elevated, and more or less zigzag where the reticulum is not devel- 

 oped; where the reticukim is developed it usually can be traced. The reticulum, although 

 the radial structures are important in its composition, is secondarily thickened and becomes 

 flaky in appearance. The development of flakes is by tangential and horizontal thickening, 

 thereby contrasting with P. mayeri, in which the radial structures are more conspicuous. 



The septa, pali, and columella of both species are similar in arrangement. 



The difference between the two, therefore, consists in the greater development 

 of the radial structures in the reticulum of P. mayeri, while in P. viridis there is a 

 greater development of the tangential and horizontal structures, and there is in 

 the latter a membranous wall, which may be zigzag. (See note at end of discussion 

 of P. mayeri, page 197.) 



Stations, Murray Islands. — Southeast reef, line I, 600 and 1,000 feet from shore. 



Distribution. — Fiji Islands; Murray Island. 



12. Porites densa, new species. 

 Plate 8g, figures 2, 2a, 2b, specimen from Murray Island. 



The following is a description of this species : 



Corallum with incrusting base; edge shows younger growths over the older; upper sur- 

 face irregularly rounded, but not thrown into gibbosities or rising into lobes or ridges. 



Calices conspicuous; diameter measured between thecal summits, up to 2.5 mm. The 

 fossae are pits, sunk into a wide mural reticulum. Diameter of the pits 0.75 to i mm.; 

 reticulum up to 1.5 mm. across; the width of the reticulum therefore exceeds the diameter of 

 the calicular pits. 



The mural trabeculae usually project above the reticulum so as to form a traceable ridge; 

 their ends are irregular in shape and size, but radially compressed and incompletely fused. 



Septa usually 12, sometimes 1 1, in number, thick, considerable irregularity in arrange- 

 ment, interseptal loculi narrow, irregular in size. Usually 2 lateral pairs, a solitary (dorsal) 

 directive, and a ventral triplet may be recognized, but one member of a pair may be short, 

 rendering the pair-fusion incomplete. Whether the short member of the pair is dorsal or 

 ventral with reference to the long member seems inconstant. The short septum, however, is 

 thick. There is irregularity in the condition of the triplet, but the lateral members are rarely 

 fused by their inner ends to the directive. 



The outer synapticular ring is strongly developed. It occurs somewhat below the upper 

 edge of the mural trabeculae and forms a coarse inner wall. Frequently an irregularly shaped 

 tooth, granulate on the end, stands up on tiie septal margin at the inner edge of the ring; or 

 a flattish, thick tooth may project inward, sloping upward at a relatively low angle. There 

 is conspicuous irregularity in the septal teeth, but the persistent presence of certain teeth, 

 which project inward in nearly horizontal planes or incline upward at low angles, is striking. 

 Between the synapticular ring and the mural trabeculae the septa are greatly thickened, with 

 the result that the mural, synapticular, and outer septal structures form a relatively dense 

 reticulum between adjacent calicular fossae. Because of the subhorizontal teeth, the reticu- 

 lum presents a flaky appearance. 



Deeper down in the calice one or tv/o subhorizontal teeth project inward on each 

 septal margin. There are no definitely developed pali, but on the inner ends of some 

 septa are irregularly shaped knots. Tlie inner synapticular ring is irregular in development, 

 rarely complete. Columellar tangle irregular in development, composed of thick, irregularly 

 bent, fusing prolongations from the inner septal ends and some synapticulae. Because of the 

 irregularity in the length of the septa, the incompleteness of the inner synapticular ring, and 

 the irregularity of the septal prolongations into the columellar tangle, the inner ends of 

 interseptal loculi are correspondingly irregular. 



Usually there is a columellar tubercle, represented by an axial knot rising above the 

 columellar tangle, but there is no persistent axial trabecula terminating in a tubercle, as in 



