130 COLLECTIONS FROM. MELANESIA. 



determine to some extent its range of variation : this, as we might 

 have expected, is most markedly presented by the characters of the 

 spinous protuberances formed by the hypertrophy of some of the 

 granules on the abactinal surface ; the smallest specimen is without 

 any special spines. Of three larger and subequal specimens, that 

 which is a little the smallest has a more prominent granule deve- 

 loped here and there along the middle lines of the rays, and some 

 six, stdl more prominent, at the centre of the disk; the other two 

 have much more prominent spinous granules at what may be called 

 the base of the rays, and some smaller protuberances around the 

 centre of the disk ; these latter are, in the largest specimen of all, 

 quite inconspicuous, li is about equal to 2 r ; 11=72, 58'; r=34, 27. 



Arms 29 or 26 millim. wide at the base, narrowing hardly at all 

 till quite near their end ; marginal plates very well developed, equal 

 in either series, and 13 or 14 in number ; pedicellarisB scarce. 



The central region of the disk is not distinctly elevated ; with 

 increase in size the ossicles of the abactinal surface become less 

 closely packed than in the smaller forms ; and three rows of ossicles 

 can be quite distinctly made out; the investing granulation is not 

 especially coarse ; the intervening pores may be set singly or dis- 

 posed in groups of three or four. With increase in size, likewise, 

 the boundary lino between the two sets of marginal plates becomes 

 more distinct ; from the angle of the arm outwards the supero- 

 marginals increase in breadth till the last two or three, but they are 

 always at least twice as long as they are broad ; the terminal two 

 or three touch in the middle line. The iniero-marginals are a little 

 stouter, but have otherwise much the same proportions as the upper 

 series. 



The intermediate plates are distinct from one another and are 

 covered by large distinct granules. The innermost row of adainbu- 

 lacral spines are 6 or 7 in number, and are more delicate than the two 

 stouter ones which are placed outside them ; those of the outermost 

 row are smaller and more irregular, and are not easily distinguished 

 from the granules of the ventral plates. 



Madreporic plate rather large, distinct, 4 to \ r distant from the 

 centre ; the anus often distinguished by its periphery of eight or 

 ten small plates. 



The dried specimens are yellowish or light slate-coloured ; but 

 there is no information as to what is their colour when alive or 

 fresh. 



The species is very distinct from P. dilatatus of Perrier, which 

 species has perhaps been founded on forms which were only varieties 

 of the Astrogonium miliare of Gray. 



Thursday Island, Torres Straits, 3-5 fms. ; sand. 



1!». Dorigona longimana. 

 Pentagonaster longinianus, Perrier, p. 228. 

 Percy Island, Queensland ; Prince of Wales Channel, Aug. 1881, 

 7 fms. 



