198 PAPERS FROM THE DEPARTMENT OF MARINE BIOLOGY. 



8. Porites somaliensis Gravier. 



Plate 87, figures 2, 2a, lb, specimen from Cocos-Kceling Islands. 

 191 1. Porites somaliensis Gravier, Ann. Inst. Oceanograph., vol. 2, fasc. 3, p. 80, plate 11, figs. 46-48. 



This species is represented by one small specimen and fragments of two large 

 ones. As the succeeding description is based on all the material and is supple- 

 mented by a photograph by Dr. Wood Jones, it is composite. 



Corallum forms sulispherical heads truncated on the lower surface where attached; some 

 radiating swellings and intervening depressions. Diameter up to 17 cm; height, up to 12 cm. 



Calices polygonal, distinct, superficial near lower edge of living tissue, deeper on upper 

 portion of corallum. Diameter from i to 1.5 mm., usually about 1.25 mm. 



Wall straight, thin, continuous or interrupted, usually with about twice as many erect, 

 frosted denticles as there are septa. The denticles are frequently compressed in radial 

 planes, but sometimes are irregularly shaped, frosted rods. In places on the upper surface 

 the denticles are small, irregular, and only slightly prominent. 



The septal arrangement and structure is constant for all parts of the corallum, but there 

 is considerable variation in thickness of the skeletal elements, the development of the septal 

 denticles, and the depth of the calices. There are the usual 1 2 septa, which are arranged into 

 a solitary directive, 4 lateral pairs, and a directive triplet, the lateral ot which are not fused 

 by their inner ends, but are fused by a transverse membrane which rises above the level of the 

 columellar tangle, resulting in a trident (according to the terminology proposed by Bernard). 

 Between each palar trabecula and the wall is a single septal trabecula which usually forms a 

 distinct septal denticle (granule) detached from the wall. Between the granule and the wall 

 the ends of the septa are usually bifurcate. The septal faces are granulate. This scheme is 

 constant. 



On the upper surface the septa are thin, less than Iialf as thick as the width of the inter- 

 septal loculi; they begin an appreciable distance below the upper edge of the wall. The 

 septal denticles are not prominent, arc irregular in shape, and the outer synapticular ring is 

 imperfectly developed. The pali on the inner ends of the lateral pairs are tall, reaching the 

 level of the upper edge of the wall, erect, and slender; the other pali are variable in development 

 or absent, more often developed on the two directives than on the laterals of the triplet, but 

 occasionally present on one or both of the latter. The transverse membrane joining the inner 

 ends of the triplet to one another has been mentioned. 



Near the lower edge of the living tissue the calices are shallow, the septa are thick, 

 densely beset with spinulose granulations, and the interseptal loculi are narrow. The septal 

 denticles are detached from the wall and so tall that they reach the level of the mural edge. 

 Occasionally two septal denticles are present, the inner being the smaller. The outer 

 synapticular ring is not always complete, but is more developed than on the upper surface. 

 There are usually 6 pali which reach the same level as the wall and the septal denticles, 

 but there is marked variation in the triplet, on which there may be I, 2, or occasionally 3 pali; 

 when 2 are present usually it is the one on the directive which is suppressed. 



The palar ring of synapticulx is nearly or entirely complete; it, with the compressed 

 columellar tubercle and the radii joining the latter to the inner ends of the septa, forming the 

 columellar tangle. The top of the tubercle is well down within the calices on the upper 

 surface, but is prominent near the edge of the living tissue. 



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

 "The most abundant coral in the atoll, the one that by its dead remains forms the bulk 

 of the solid material of the dry land. The specimen is from the barrier. The color varies 

 from purple, purple brown, olive brown, olive green, and yellow brown to yellow." 



Porites somaliensis has a suggestive resemblance to Porites lutea M. Edw. from 

 the Fiji Islands, notes on the type of which immediately follow. 

 Distribution. — East coast of Africa; Cocos-Keeling Islands. 



9. Porites lutea Milne Edwards. 



Plate 88, figures I, la, iJ, type of species, the specimen identified by Dana as Porites conglomerata. 



1846. Porites conglomerata Dana, U. S. Expl. Exped., Zooph., p. 561, plate 55, figs. 3, 3a. 



i860. Porites lutea Milne Edwards, Hist. nat. Corall., vol. 3, p. 180. 



1905. Porites fidjiensis secunda Bernard, Cat. Porites Indo-Pacific, p. 44, plate 3, figs. 1-4; plate 11, fig. 3. 



1905. Porites fidjiensis decima Bernard, Cat. Porites Indo-Pacific, p. 52 (see also p. 244). 



