32 MADREPORARIA. 
** Branches rarely over | cm. thick. 
5. Madrepora gracilis. 
Madrepora gracilis, Dana, Zoophytes, p. 482, pl. xli. fig. 3; M.-Edwards & Haime, Coralliaires, t. iii. 
p- 147; Quelch, ‘ Challenger’ Reef Corals, p. 158 (part.) ; Duncan, Journ. Linn. Soc. Lond. 1886, 
vol. xxi. p. 19; Rathbun, Proc. U.S. Nat. Mus. 1887, vol. x. p. 16 (non Ortmann, Zool. JB. 1889, 
Bd. iv. p. 503). 
? Madrepora pustulosa, Quelch (non M.-Ed. & H.), ‘Challenger’ Reef Corals, p. 158. 
Corallum arborescent, spreading ramose; branches slender, 6 to 10 mm. thick, arcuate, 
gradually attenuate. Axial corallites 2 cm. long and broad ; radial corallites equal, rather 
crowded, stout compressed nariform, small (2 mm, long), aperture narrow, star distinct, the 
directive septa broadest. The radial corallites become quite short at a distance of 10 cm. 
from the apex. Surface of the ccenenchyma appears smooth, wall finely striate. (Dana.) 
The following are some of the more important details of the Challenger specimens :— 
Axial corallites 2 mm. diameter, very little prominent, aperture large; septa in two well- 
developed cycles, the directives broadest. Radial corallites mostly 4 mm. long and 1 mm. 
diameter, compressed tubo-nariform, or tubular with very oblique aperture; a few much 
smaller and shorter ones scattered between the others. Corallum very porous in section, 
surface spongy-echinulate, wall costate, coste spinose, particularly near the base. 
Indo-Pacific Ocean : Ceylon to Sulu Sea and Fiji. 
a-b. Amboina. H.M.S. ‘Challenger.’ 86. 12.9. 270 & 272. 
?c. Levaku, Fiji. H.M.S. ‘Challenger.’ 86. 12.9. 239. (= WM. pustulosa, Quelch.) 
6. Madrepora heteroclados. 
Madrepora cf. ramiculosa, Ortmann, Zool. JB. 1888, Bd. iii. p. 153. 
Corallum shrubby arborescent, with erect little-spreading subdivisions or with divaricate 
and curved branchlets; sometimes both forms occur in the same specimen. Branches up 
to 10 cm. long and 1 em. thick at the base; divisions spiciform, erect or spreading 
obliquely with arched spiciform branchlets, 3°5 em. long; marginal twigs about 5 mm. thick 
at a point 2 cm. from the apex. Axial corallites 1°5 to 2 mm. diameter, 1 mm. exsert; wall 
thickened, margin slightly rounded. Radial corallites spreading blunt-nariform, with 
convex lower and horizontal upper margin, or spreading tubular with an oblique aperture ; 
a smaller number are gutter-shaped. Length 2 mm., diameter 1-2 to 1°5 mm., wall thin but 
firm. Nearer the base of the branchlets many of the corallites are hooked-nariform with 
a thicker wall, others are hemicotyloid to subimmersed. Star not prominent, but the 
directive septa may be broad. Corallum rather dense; surface dense and tabulato-echinulate ; 
wall finely striato-echinulate. In the divaricately-branched forms the subdivisions sometimes 
become fused together. 
Pacific Ocean: Pelew Islands, Ponapé, Tahiti. (Strassburg Museum.) 
