MADEEPOEA. 136 



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, n. 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, c. Rocky Island. Saville-Kent Coll. 92. 6. 8. 41 & 48. 



6. Subgenus TTLOPOEA. 



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 Eumadrepora ; the M. humilis group is related on 

 the one hand to Isopora, 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, pi. xl. fig. 3 ; M.-Edwards & Haime, Coralliaires, t. iii. 

 p. 143 ; VerriU (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 ; Queleh 

 (part.), 'Challenger' Eeef Corals, p. 150; Eathbun (part.), Proc. U.S. Nat. Mus. 1887, vol. x. 

 p. 17. 



Corallum shrubby arborescent, in spreading clumps of stout branches. Branches often 

 2-5 cm. thick, divaricate, terete; summit branchlets 1 to 2 cm. thick; apex conical in some 

 specimens, more pointed in others. Axial eorallite 3 to 4 mm. broad and 1 to 3 mm. exsert ; 

 wall about 1 mm. thick. On branches with a conical apex the axial eorallite 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. 



t2 



