MADREPORA. 135 
more spreading near the base. Length 1 to 4 mm., diameter 1 to 15 mm. Aperture large ; 
wall thin compared with other species of the subgenus. Surface finely clothed with longi- 
tudinal series of dentate plates. 
The species differs from all others of the subgenus in the possession of thin-walled 
radial corallites. 
A specimen in the Berlin Collection, referred by Rehberg to M. incrustans, un. sp., agrees 
with my type specimen. 
Pacific Ocean: Tongatabu, Great-Barrier Reef. 
a. Tongatabu. J. J. Lister, Esq. [P.]. 91.3.6.7. (Type.) 
b,¢. Rocky Island. Saville-Kent Coll. 92. 6. 8. 41 & 48. 
6. Subgenus TYLOPORA. 
Axial corallites broad, usually hemispherical, sometimes slightly exsert at the margin. 
Corallum cespitose, bushy, or corymbose. Branchlets blunt at the apex. The radial corallites 
are usually thick-walled, with or without a rounded margin. Septa usually well developed. 
The M. nobilis group shows an affinity to Humadrepora; the M. humilis group is related on 
the one hand to Jsopora, and on the other, through M. brueggemanni var. uncinata, to the 
variablis group of Conocyathus. 
A. Wall of radial corallites thick, but porous ; margin not rounded. 
a. Radial corallites spreading tubular, dimidiate or somewhat funnel-shaped, always broader 
at the apex than at the base. 
136. Madrepora nobilis. 
Madrepora nobilis, Dana, Zoophytes, p. 481, pl. xl. fig. 3; M.-Edwards & Haime, Coralliaires, t. ii. 
p. 143; Verrill (part.), Bull. Mus. Comp. Zool. 1864, vol. i. p. 40; ibid. Proc. Essex Inst. 1866, 
vol. v. p. 20; ibid. 1869, vol. vi. p. 68; Studer, Mitth. naturf. Ges. Bern, 1880, p. 18 ; Quelch 
(part.), ‘Challenger’ Reef Corals, p. 150; Rathbun (part.), Proc. U.S. Nat. Mus. 1887, vol. x. 
pode 
Corallum shrubby arborescent, in spreading clumps of stout branches. Branches often 
2°5 em. thick, divaricate, terete; summit branchlets 1 to 2 em. thick ; apex conical in some 
specimens, more pointed in others. Axial corallite 3 to 4 mm. broad and 1 to 3 mm. exsert ; 
wall about 1 mm. thick. On branches with a conical apex the axial corallite is only slightly 
exsert. Radial corallites much crowded, nearly erect, or somewhat appressed ; different speci- 
mens and different parts of the same specimen show a considerable variation in the angle at 
which the corallites are placed. The majority are half-tubular or dimidiate, with the wall a 
little thickened, not compressed, about 3 mm. long and 1:5 mm. diameter across the lip. 
Others between are short, labellate, or nariform, with a thin wall, or altogether immersed. 
r2 
