72 PERCY SLADEN TRUST EXPEDITION 



Klunzinger's figured type of this species measures 16 x 12 x 8 cm. Its distinguishing 

 charactei's are as follows : (l) septa in four orders but the fourth incomplete, the maxi- 

 mum numbers of quaternaries counted being ten ; (2) six to ten septa meeting the 

 columella ; (3) the remaining septa very narrow ; (4) columella quite rudimentary. 

 In general appearance the specimen resembles L. roissyana, but its real position in 

 the genus cannot be settled till its polyps are examined. 



The single specimen from Hulule which Gardiner has referred to L. immersa is 

 identical with Klunzinger's example. 



GENUS DIPLOASTREA, NDU.GEN. 



1816. Asirea (pars), Lamarck, Hist. Anim. sans vert., ii, p. 257. 



1850. Astrea (pars), Milne Edwards and Haime, Ann. Sci. Nat., Zool., 3'= ser., xii, p. 97. 



1857. Heliastrma (pars), Milne Edwards and Haime, Hist. Nat. CoralL, p. 456. 



1904. Orhicella (pars), Gardiner, Fauna Geogr. Maldives and Laccadives, ii, p. 774. 



■ This genus has been created for Orhicella minikoiensis, Gardiner. Its characters 

 are as follows : 



Corallum. Incrusting or massive. Corallites circular not projecting. Walls fused 

 and perforate, hence peritheca almost absent. Calices shallow. Septa in not less than 

 two orders, the first two entocoelic, each consisting of twelve septa, exsert, much thickened 

 towards their outer ends. Columella formed of twisted trabeculae from septal margins. 

 Calicular dissepiments oblique. 



Polyps. Close together with narrow edge-zones, no coenosarc. Mesenteries in not 

 less than two cycles, each of twelve couples, usually directly continuous from polyp to 

 polyp, primaries meeting stomodseum ; all with filaments. Mesoglsea thick. Tentacles 

 corresponding in number and position with entocoeles and exocoeles. 8tomoda3um short, 

 laterally compressed with two directive grooves. Multiplication by budding. 



Remarks. Owing to the presence of two directive couples of mesenteries 0. mini- 

 koiensis has to be separated from the old genus Orhicella (Group II) and placed in Group I. 

 But it differs from all other described genera of this sub-family in possessing, in its adult 

 polyps, double the usual number of couples of primary and secondary mesenteries, viz. 

 12 in each cycle, and a highly thickened mesenterial mesoglgea, the mesenteries in 

 consequence presenting an unique appearance in transverse section. The perforate 

 nature of the corallite-walls indicates a probable variation of Diploastrea to the Perforata, 

 but the perforations are larger and fewer than in the latter group and are irregular. 



Distribution. Red Sea, Indian and Pacific Oceans. 



1. Diploastrea heliopora (Lamarck) (PL 20, figs. 7 and 8 ; 34, fig. 9). 



1816. Astrea heliopora, Lamarck, Hist. Anim. sans vert., ii, p. 265; 2'* edit., p. 415. 



1824. Astrea heliopora, Lamouroux, Encycl., Zooph., p. 128. 



1848. Astrea heliopora, Milne Edwards, Grande edit. Regne Anim. Cuvier, Zooph., pi. 84 ter, figs. 1, la and b. 



1850. Astrea heliopora, Milne Edwards and Haime, Ann. Soi. Nat., Zool., 3*= ser., xii, p. 99. 



1857. Heliastrma heliopora, Milne Edwards and Haime, Hist. Nat. Corall., ii, p. 459. 



1904. Orhicella minikoiensis, Gardiner, Fauna Geogr. Maldives and Laccadives, ii, p. 774, pi. 63, fig. 35, 



1907. Orhicella minikoiensis, Vaughan, Proc. U.S. Nat. Mus., xxxii, p. 252. 



