1s84.] speciks of oreaster. 67 



Oreaster mammillatus. 



Oreaster mammillatus, M. Tr, Syst. Ast. p. 48. 



R=2"7r. Disk moderately elevated, the elevation not confined 

 to the central portion ; arms moderate, rather narrow than wide. 

 Lophial line marked hy the greater size, and consequent prominence 

 of some of its ossicles ; no spines, however, are developed thereon. 



About 18 superomarginal and 20 inferomarginal plates; the 

 latter are confined to the ventral surface ; the former are, ordinarily, 

 obtusely conical, and the free end is bare of granules, but there is 

 no reason for supposing that these have the functions of spines ; 

 similar blunt tubercular growths are to be found on the more proxi- 

 mal inferomarginals. 



Adambulacral spinulation diplacanthid ; six well- formed spines, 

 not sharp at their tips, and longer mesially than laterally, occupy the 

 inner row ; in the outer there are two or three stout short spines ; 

 when tliere are three, the middle one is generally the stoutest. 



The arrangement of the ossicles of the ventral face is a little 

 obscured by the coarse granulation by which they are covered ; here 

 and there, and especially towards the edges of the disk, some of the 

 granules come to form quite distinct tubercles ; the granulation on 

 the marginal plates is sufficiently coarse. 



From the nodal points of the ossicles of the back there arise 

 tubercular processes, hardly one of which deserves to be called 

 spinous ; the pore-areas between are considerable, not always dis- 

 tinctly separated from one another ; three rows are ordinarily to be 

 detected along the side of the arms, and of these the lowest is the 

 most extensive. The ossicles on the apical region are swollen and 

 tubercular. 



The madreporite is irregularly shield-shaped, and placed nearly 

 halfway between the centre and the edge of the disk. 



Colour, stony grey. 



Measurements: — R 118, r44 ; greatest breadth of arm 46, 



Hab. Red Sea ; Mauritius. 



Oreaster valvtjlatus. 



For a careful description of this form from New Holland, see the 

 account given by Miiller and Troschel ; it appears to be most re- 

 markable for its long valvular pedicellarise. 



Oreaster granulosus. 



Pentaceros granulosus, Gray, P. Z. S. 1847, p. 75. 



A triplacanthid unarmed species with the disk depressed, and the 

 habit as much of Qoniodiscus as of Oreaster. 



R = 2*2 r. Disk depressed ; arms rather wide at their base, and 

 not very acute at their tip ; lophial ossicles not prominent, and 

 apical spines, as indeed all spines, completely wanting. 



About 14 supero- and infero-marginal plates ; both sets take part 

 in forming the sides of the arms, are well developed in proportion to 

 the general size of the Starfish, but are always without any spines 

 whatsoever. 



5* 



