MADREPOEA. 59' 



The moderate variation in size of the axial corallites, and the variation in length of the 

 proliferous corallites or branchlets, according to age, has probably led to this species being 

 described under several names. It is significant that all the types of all the forms (? M. pus- 

 tulosa, Edw. & H.) come from the Red Sea. 



Indian Ocean : Red Sea, Keeling Island. 



a, b. Keeling Island. H. O. Forbes, Esq. [C.]. 84. 2. 16. 50 & 51. 

 c-d. ? ? 93. 4. 7. 82 & 83. 



39. Madrepora gravida. 



Madrepora gravida, Dana, Zoophytes, p. 470 ; M.-Edwards & Haime, Coralliaires, t. iii. p. 137 ; 

 Verrill, Bull. Mus. Comp. Zool. 1864, vol. i. p. 40 ; Studer, Mitth. naturf. Ges. Bern, 1880, 

 p. 18. 



1 Madrepora hraeliyclados, Ortmann, Zool. JB. 1888, Bd. iii. p. 149, pi. vi. fig. 1. 



Corallum arborescent, erect or subhorizontal, massive, sometimes with an elongate 

 incrusting base. Form very variable ; sometimes the main branches are erect, terete, 3 cm. 

 diameter, with strongly arcuate branches, giving the appearance of a pine-tree, at others the 

 main branches are flattened, extend chiefly in one plane, and may be 10 cm. broad. The 

 branches bear a very large number of short, subcylindrical branchlets, chiefly on the upper 

 surface. The majority are \'o to 2 cm. long and 0'7 cm. diameter, chiefly simple, but may 

 be branched or proliferous at the apex. Axial corallites 2'5 to 3 mm. diameter, thick-wailed, 

 varying in prominence from to 2 mm. in different specimens. Radial corallites of the 

 branches all immersed or subimmcrsed ; those of the branchlets may or may not be immersed 

 in the basal half, but those of tlie distal half are always prominent and subequal. They vary, 

 however, considerably in form, and may be nariform, labellate, tubular, or dimidiate ; some- 

 times all forms occur in difierent parts of the same specimen. The usual type is crowded 

 nariform or short tubular, with the inner part of the wall more or less incomplete, and the 

 outer part thickened a little; length 1 to 2 mm., mostly under 1-5 mm.; breadth 1-5 to 



2 mm. The posterior (or inferior) surface of the corallum bears apprcssed, flattened, half- 

 tubular corallites chiefly, which are irregularly scattered, and may be 3*5 mm. long, but 

 always have a narrow aperture; there are not many immersed corallites on this surface, 

 excepting near the base, where they are much smaller than those above. Corallum rather 

 porous ; surface openly reticulate and echinulate ; wall striato-echinulate. The corallites 

 usually have 12 well-developed septa, those of each cycle subequal in the axial corallites, but 

 the directives are usually more prominent in the radial ones. 



Indo-Pacific Oceau : Singapore, Fiji. 



a, b. ? Purchased. 56. 2. 18. 28 & 34. 



c. Singapore ? Purchased. 53. 6. 7. 3. 



d. Singapore. Purchased. 40. 5. 15. 2. 

 e,f. ? ? 93. 4. 7. 68 & 69. 



