102 MADREPORARIA, 
93. Madrepora arcuata. (Plate XII.) 
Madrepora arcuata, Brook, Ann Mag. N. H. 1892, vol. x. p. 452. 
Corallum stalked, flabellate or subvasiform. The largest specimen is 50 em. long, and 
consists of a thin plate-like flabellum, extending obliquely from a round pedicel 5 cm. 
in diameter. The proximal portion, 20 cm. in length, is only about 10°5 em. wide, the distal 
part forms a fan-shaped growth 34 cm. across, rounded anteriorly, and with the posterior 
margins a little incurved; the thickness from the under surface to the apex of the 
branchlets on the anterior surface is only 2 cm. The under surface consists of a close 
reticulum of slender branches with narrow and elongate spaces between ; diameter of the 
branches 6 mm. The under surface is practically without branchlets, and the branches are 
covered with much appressed tubular corallites; near the base the majority become short 
and finally immersed, and immersed corallites occur also in the lines of fusion. On the upper 
surface the branchlets are slender, arcuate and crowded, apices 5 mm. apart, often less in the 
case of proliferous apices. The branchlets are usually about 1:2 cm. long and 4 mm. thick, 
including the radial corallites; they are arranged in single or double series along the upper 
surface of a branch, some are simple, in other cases 2 to 5 twigs arise from a common base. 
Axial corallites cylindrical, 1-5 mm. diameter and about 1°5 mm. exsert ; wall porous and 
finely striate. Radial corallites tubo-labellate at an angle of about 45° ; lip pointed or gutter- 
shaped; length 2°5 mm., diameter 1 mm. Star very imperfect, the directive septa scarcely 
recognizable. Corallum very porous; surface openly spongy and echinulate; wall thin, 
striato-reticulate, echinulate below. 
In one of the specimens which appears to have grown erect the posterior margins of the 
flabellum have arched inwards, so as to overlap and become fused together, but below the 
point of fusion a space occurs, the floor of which consists of branchlets which at an earlier 
period formed part of the upper surface of the colony. The specimen is about 14 cm. high 
and 20 cm. diameter; the corallites on the under surface are shorter and more spreading than 
usual. A third specimen in the collection consists of 6 or 8 small colonies forming a cluster 
on a piece of dead coral; the largest colony is about 9°5 em. high and 14 em. broad. 
Pacific Ocean: Samoa Islands. 
a, 6. Samoa Islands. Purchased. 62. 1. 27.4 & 5. nf 
c. Samoa Islands. Rev. S. J. Whitmee [P.]. 75. 10.2.9. } pi 
94. Madrepora microclados. 
Heteropora microclados, Ehrenberg, Corallenth. d. roth. Meeres, p. 109 (part.); non IM. microclados, 
auctt. 
Madrepora flabelhformis, M.-Kdwards & Haime, Coralliaires, t. iii. p. 157; Ortmann, Zool. JB. 1888, 
Bd. iii. p. 153; ibid. 1889, Bd. iv. p. 511 (non Briiggemann, Phil. Trans. 1879, vol. clxviii. 
p- 575; non Ridley, Ann. Mag. N. H. 1883, vol. xi. p. 259). 
