MADREPORA. 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, Kdw. & 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. 
? Madrepora brachyclados, Ortmann, Zool. JB. 1888, Bd. iii. p. 149, pl. 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 1-5 to 2 em. long and 07 em. diameter, chiefly simple, but may 
be branched or proliferous at the apex. Axial corallites 2°5 to 3 mm. diameter, thick-walled, 
varying in prominence from 0 to 2 mm. in different specimens. Radial corallites of the 
branches all immersed or subimmersed ; those of the branchlets may or may not be immersed 
in the basal half, but those of the 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 different parts of the same specimen. The usual type is crowded 
nariform or short tubular, with the inner part of the wall more or Jess incomplete, and the 
outer part thickened a little; length 1 to 2 mm., mostly under 1°5 mm.; breadth 1°5 to 
2mm. The posterior (or inferior) surface of the corallum bears appressed, 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 Ocean: 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. i Ti 93. 4. 7. 68 & 69. 
