102 MADREPORAEIA. 



93. Madrepora arcnata. (Plate XII.) 



Madrepora arcuata. Brook, Ann Mag. N. H. 1892, vol. x. p. 452. 



Corallum stalked, flabellate or subvasiform. The largest specimen is 50 cm. 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 cm. 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 cm. high and 14 cm. broad. 



Pacific Ocean : Samoa Islands. 



Samoa Islands. Purchased. 62. 1. 27. 4 & 5. -j 



Samoa Islands. Rev. S. J. Whitmee [P.]. 75. 10. 2. 9. J ^^P^^* 



94. Madrepora microclados. 



Heteropora microclados, Ehrenberg, Corallenth. d. roth. Meeres, p. 109 (part.) ; non M. microclados, 



auctt. 

 Madrepora Jlahelliformis, M.-Edward8 & 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 Bidley, Ann. Mag. N. H. 1883, vol. xi. p. 259). 



