66 PERCY SLADEN TRUST EXPEDITION 



Locality. Rotuma (2). Milne Edwards and Haime's type specimens of this species 

 are missing from the Paris Museum. 



LEPTASTREA (Milne Edwards and Haime). 



1848. Leptastrea, Milne Edwards and Haime, Compt. rend. I'Acad. Sci., xxvii, p. 494. 



1848. Baryastrea, Milne Edwards and Haime, Compt. rend. I'Acad. Sci., xxvii, p. 495. 



1857. Leptastrcea, Milne Edwards and Haime, Hist. Nat. Corall, ii, p. 493. 



1857. Baryastrcea, Milne Edwards and Haime, Hist. Nat. Corall., ii, p. 512. 



1879. Leptastrcea (pars), Klunzinger, Korall. Roth. Meer., iii, p. 43. 



1884. Leptastrcea, Duncan, Journ. Linn. Soc, London, Zool., xviii, p. 119. 



1884. Baryastrcea, Duncan, Journ. Linn. Soc. London, Zool., xviii, p. 119. 



1886. Leptastrcea, Quelch, Reef Corals, Challenger Reports, Zool., vol. xvi, pt. xlvi, p. 108. 



1899. Orbicella (pars), Gardiner, Proc. Zool. Soc. London, p. 751. 



1901. Leptastrcea, Studer, Zool. Jahrb., xl, p. 402. 



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



Corallum, Incrusting, convex or round, sometimes raised into hillocks, dense and 

 usually heavy. Corallites polygonal, oval or round, not projecting or at most up to 

 1"75 mm., one side usually more than the other, arranged close together with little or no 

 peritheca, as a rule separated on the surface by narrow furrows, which are always 

 polygonal around corallites. Walls fused, dense, varying from '5 to 3 mm. in thickness. 

 Calices oval, round or polygonal, sometimes laterally compressed and distorted, varying 

 considerably in diameter in the same specimen from 2 to 5 "5 mm. and in depth from almost 

 flat up to 3 "6 mm. Septa in four orders, the first three always complete, upper margins 

 usually flat, primaries meeting columella ; the fourth order complete or incomplete, some- 

 times a few quinaries, last order exocoelic. Costse seen as low flat ridges when corallites 

 project. Columella varying from very thin to a third or half the width of calices. 

 Calicular dissepiments horizontal or somewhat oblique, about "75 or 1 mm. apart. Giant 

 corallites present. 



Polyps. Oval or circular, upper margins somewhat polygonal, varying in size. 

 Edge-zones absent when corallites do not project, and little or no intervening coenosarcal 

 regions owing to close approximation of corallites. Mesenteries in three or four cycles, 

 the first two of six couples each, the third when complete of twelve couples but often 

 incomplete, quaternaries when present few in number ; all with filaments. Tentacles 

 corresponding in number and position with entocoeles and exocoeles. Stomodseum short, 

 usually compressed laterally, with narrow directive grooves. Entocoelic pleats similar 

 in general shape to those of Galaxea but less broad and only a few sub-divided. Multipli- 

 cation by budding. 



Remarks. This genus comes nearer Galaxea than any other described genera, as 

 may be seen from the following comparison of L. roissya^ia and G. musicalis. (l) The 

 terminal batteries of entocoelic tentacles are feebly developed in both species, with neither 

 thickened ectoderm nor closely-packed nematocysts, whereas those of the exocoelic 

 tentacles are well defined with nearly the same shape and relative size. (2) The endoderm 

 of exoccelic tentacles is so much distended as to fill their lumina in the regions of the 

 terminal batteries. (3) The stomodseum is much compressed laterally and its wall 

 distorted by the ingrowth of septa. (4) Tertiary couples of mesenteries present. (5) The 



