60 MADEEPOEAEIA. 



40. Madrepora affinis. (Plate XXVIII. fig. F.) 



Madrepora omata, Brook (non Defrance), Ann. Mag. N. H. 1891, vol. viii. p. 464. 



Corallum stout, arborescent ; branches elongate, below laxly divided, 2 to 3 cm. thick, 

 often oval in section, divided into a cluster of branches at the apex ; the whole densely 

 covered with short ramiculi 8 to 13 mm. long and 5 to 7 mm. thick, and about 1 cm. apart, 

 with numerous very short or immersed corallites between. Axial corallites 3 mm. diameter, 

 1 to rS mm. exsert ; wall thick, margin rounded, aperture about 1 mm. Radial corallites 

 short, round, nariform, with thickened wall and rounded margin, outer wall a little convex, 

 1'5 to 2-0 mm. long and nearly 2 mm. diameter. On the stouter ramiculi two or three 

 corallites become 3 mm. long and bear three or four buds. The ramiculi are as numerous 

 on the inferior (posterior) surface of the branches as elsewhere, but are usually shorter. 

 Star usually indistinct, but one or both directive septa may be moderately prominent. 

 Corallum moderately porous ; surface spongy, echinulate ; wall striato-reticulate and echi- 

 nulate. 



The name M. omata, under which this species was originally described, had previously 

 been given by Defrance to a fossil species, and is therefore now replaced by M. affinis. The 

 species is closely allied to M. gravida, and may be only a well-marked variety of it. So long 

 as the type specimens were the only ones available for comparison with M. gravida there 

 appeared little difficulty in distinguishing the species from one another. More recently, 

 however, a considerable number of specimens from the Great-Barrier Reef area and the 

 Macclesfield Bank have been acquired, some of which show a closer approach to the habit of 

 M. gravida than was previously anticipated. Nevertheless the habit is less robust, the 

 branchlets circwmaxial, except in complanate specimens, usually not over 1"5 cm. in length, 

 and the apices of the branches are much divided. The radial corallites are shorter, stouter, 

 and more spreading than in M. gravida, and the star of septa is rarely well-developed, even 

 in the axial corallites. The corallites are rarely immersed on the basal parts of the twigs, 

 and those between the branchlets are rarely immersed on the distal parts of the corallum ; 

 they are usually more or less nariform, or have a ring-shaped border. Those which occur in 

 the lines of fusion are, h\owever, immersed, as is usually the case in such situations. 



Pacific Ocean : Great-Barrier Reef, Macclesfield Bank. 



o-c. Damley Island. \ J. B. Jukes, Esq. [P.]. 46. 7. 30. 29 to 31. (Types.) 



d^k. Cleremont Island. \ Saville-Kent Coll. 92. 6. 8. 96 to 101, 112 & 113. 



Ir^. Macclesfield Bank, 13 ftith. H.M.S. ' Penguin.' 92. 10. 17. 14 to 16. 



\ 



41. Madrewora compressa. (Plate XXXIII. fig. E.) 



Madrepora compressa, Bassett-Smit^, Ann. Mag. N. H. 1890, vol. vi. p. 452. 



Corallum forming a horizointal plate 40 cm. wide and 2'7 cm. thick, from a lateral 

 attachment. Main branches massive, vertically compressed, 3 cm. broad and 2 cm. thick, 

 (.innately divided ; the whole morie or less completely fused into a solid plate, with scattered 



