32 MADREPORAEIA. 



** Branches rarely over 1 cm. thick. 



5. Madrepora gracilis. 



Madrepora gracilis, Dana, Zoophytes, p. 482, pi. xli. fig. 3 ; M.-Edwards & Haime, CoraUiaires, t. iii. 

 p. 147 ; Quelch, ' Challenger ' Eeef Corals, p. 158 (part.) ; Duncan, Journ. Linn. Soc. Lend. 1886, 

 voLxxi. p. 19 ; Rathbun, Proc. U.S. Nat. Mas. 1887, vol. x. p. 16 (non Ortmann, Zool. JB. 1889, 

 Bd. iv. p. 503). 



? Madrepora pusttdosa, Quelch {wm M.-Ed. & H.), ' Challenger' Reef Corals, p. 158. 



Corallum arborescent, spreading ramose ; branches slender, 6 to 10 mm. thickj arcuate, 

 gradually attenuate. Axial corallites 2 cm. long and broad ; radial corallites equal, ratlier 

 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, costse 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. { = M.pustulosa,Q,vie\.ch.) 



6. Kadrepora 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 cm. thick at the base ; divisions spiciform, erect or spreading 

 obliquely with arched spiciform branchlets, 3'5 cm. 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, Ponape, Tahiti. (Strassburg Museum.) 



