66 MADREPORARIA. 



Corallum somewhat porous; surface as if worm-eaten in places, but in other parts finely 

 echinulate ; wall striate. Star prominent, particularly the directive septa. 



Indo-Pacific Ocean : Red Sea, Pelew, Ponape, N. and E. Australia, Tahiti. 



a, b. N. Australia. J. R. Elsey, Esq. [P.]. 57. 11. 18. 202 & 219. 



c. Bellona Shoal, E. of Australia. F. M. Rayner, Esq. [P.] . 62. 2. 4. 18. 



2. Subgenus ODOM'OCYATHUS. 



Corallum more or less complanate. The cylindrical axial corallites are usually provided 

 with only 6 septa, but occasionally there may be indications of a second cycle. A large 

 proportion of the radial corallites are immersed or subimmersed, the more prominent ones are 

 never completely tubular unless proliferous, usually the wall is acuminate. The corallum is 

 very porous and rough on the surface. The species of this subgenus are connected with 

 Eumudrepora through M. scabrosa &c., and with the spicifera group of Polystachys through 

 M. reticulata and its varieties. 



48. Madrepora arabica. 



Heteropora prolifera, Ehrenberg (non Lamarck), Corallonth. d. roth. Meeres, p. 112. 



Madrepora arabica, M.-Edwards & Haime, Coralliaires, t. iii. p. 145 {non Ortmann, Zool. JB. 1888, 



Bd. iii. p. 150). 

 Madrepora spinulosa, TQunzinger, Korallenth. d. roth. Meeres, Th. ii. p. 23, pi. ii. fig. 8, pi. iv. fig. 11, 



pi. ix. fig. 18. 



The following is a description of the type of Milne-Edwards : — 



Corallum arborescent, laxly branched, branches 1 to 1*4 cm. thick, divergent, not much 

 divided, except near the apex, where they bear numerous short stunted branchlets of 4 to 12 mm. 

 in length and 4 to 6 mm. diameter. All the corallites on the main branches and most of the 

 branchlets are immersed, and a little under 1 mm. in diameter. On the terminal 5 cm. of the 

 colony the corallites are short, open tubular, with a very thin wall, the inner portion of which 

 scarcely projects beyond the surface of the coenenchyma. The largest have the outer wall 2 mm. 

 in length and slightly over 1 mm. diameter. Axial corallites 2 mm. diameter, scarcely promi- 

 nent ; aperture large, with a thin irregular wall. Corallum rather dense {? probably due to 

 secondary deposition of lime) ; surface composed of vermiform ridges, echinulate, and often 

 confluent ; wall and coenenchyma near the apex consisting of sinuous and dentate plates. 

 Septa scarcely developed at all near the apex of the colony ; most of the immersed corallites 

 are practically without septa, in others 6 very narrow primaries may be recognized, of which 

 the inner directive is broadest. (The specimen is worn.) 



M. spinulosa, Klunz., is based on Ehrenberg's H. prolifera, and is not a species obtained 

 by Klunzinger himself. He appears to have been of opinion that the form might have been 

 referred to M. arabica, were it not for the fact that Milne-Edwards describes the surface of 

 his type as " pas subcostule." This, as will be seen from the above description, is scarcely 

 correct. The surface, although not subcostulate in the ordinary sense, consists of a number 

 of vermiform ridges (as in some other species), which are arranged longitudinally, but 



