Report on the zoological collections made in the Indo-Pacific Ocean ...

130 COLLECTIONS FROM MELANESIA.determine to some extent its range of variation : this, as we mighthave expected, is most markedly presented by the characters of thespinous protuberances formed by the hypertrophy of some of thegranules on the abactinal surface ; the smallest specimen is withoutany special spines. Of three larger and subequal specimens, thatwhich is a little the smallest has a more prominent granule developedhere and there along the middle lines of the rays, and somesix, still more prominent, at the centre of the dislv ; the other twohave much more prominent spinous granules at what may be calledthe base of the rays, and some smaller protuberances around thecentre of the disk ; these latter are, in the largest specimen of all,quite inconspicuous. E. is about equal to 2 r; R=72, 58 ; r—34, 27.Arms 29 or 26 millim. wide at the base, narrowing hardly at alltill quite near their end ;marginal plates very well developed, equalin either series, and 13 or 14 in number ;pedicellarise scarce.The central region of the disk is not distinctly elevated ; withincrease in size the ossicles of the abactinal surface become lessclosely packed than in the smaller forms ; and three rows of ossiclescan be quite distinctly made out ; the investing granulation is notespecially coarse ; the intervening pores may be set singly or disposedin groups of three or four. With increase in size, likewise,the boundary line between the two sets of marginal plates becomesmore distinct ; from the angle of the arm outwards the superomarginalsincrease in breadth till the last two or three, but they arealways at least twice as long as they are broad ; the terminal twoor three touch in the middle line. The infero-marginals are a littlestouter, but have otherwise much the same proj)ortions as the upperseries.The intermediate plates are distinct from one another and arecovered by large distinct granules. The innermost row of adambulacralspines are 6 or 7 in number, and are more delicate than the twostouter ones which are placed outside them ; those of the outermostrow are smaller and more irregular, and are not easily distinguishedfrom the granules of the ventral plates.Madreporic plate rather large, distinct, g to ^ r distant from thecentre ;the anus often distinguished by its periphery of eight orten small plates.The dried specimens are yellowish or light slate-coloured ; butthere is no information as to what is their colour when alive orfresh.The species is verj-^ distinct from P. dilafatiis of Perrier, whichspecies has perhaps been founded on forms which were only varietiesof the Astrof/onium miliare of Gray.Thursday Island, Torres Straits, 3-5 fms. ; sand.19. Dorigona longimana.Pentagonaster longimanus, Perrier, p. 228.Percy Island, Queensland ; Prince of Wales Channel, Aug. 1881,7 fms.