1884.] Sl'KCIES OF OREASTKR. 75 



four, well developed. All the ventral spines on the disk with one 

 or two spinous tubercles ; owing to the narrowness of the arm only 

 one row extends along the side of the adambulacral spines, and the 

 plates at .the distal end of this are without spines. 



The pore-areas of the dorsal side are distinctly marked, but vary 

 considerably in size and form ; the apical region has no central spine, 

 and the most prominent spine of the row along the lophial line is 

 not at all high ; none of the spines along the lophial line are especially 

 prominent, and they are not always separated from one another by 

 equal distances ; at the distal end of the arm they may become 

 rounded tubercles. Madreporic tubercle moderate, just outside 

 the apical region, lozenge-shaped. 



Colour (in alcohol) creamy yellow. 



R=148, 220. r=32, 53'5. Breadth of arm at base 32, 50. 



Hab. Billiton. 



Oreaster ltjetkenj, sp. nov. 



A diplacanthid form, with the appearance, were it not for the 

 shallowness of its disk, of O. reticulatus. Supero- and inferomarginal 

 spines; the ventral plates without spines, but most abundantly pro- 

 vided with pedicellarise. 



R=2"4 r. Disk not elevated : arms, where distinct from the disk, 

 rapidly tapering ; most of the supero- and of the inferomarginal 

 plates provided with spines ; of the lophial series the apical spines 

 are alone well developed ; short, but quite distinct spines developed 

 at all the angles of the poriferous area?. 



There are about 21 plates in either series along the side of the 

 arm, but the whole of the side of the arm is occupied by the superior 

 set. The disposition of the spines on these plates is exceedingly 

 irregular : only about half of the plates are spiniferous ; spines on the 

 infero marginals are rarer and much less developed. In both series 

 plates without spines will be found to carry, perhaps as many as 

 three, pedicellarias. 



Of the adambulacral spines the inner row has 8 for each plate ; 

 these are not very delicate, nor are they exceedingly different in 

 length ; between each set is an elongated forcipiform pedicellaria. 

 The outer row has, as a rule, two pretty stout spines on each plate. 

 The ventral plates are remarkably distinct from one another, the 

 granules often larger, the valvular pedicellarise of some size, numerous, 

 especially in the neighbourhood of the ambulacra. The ventral 

 plates which extend along the lower side of the arm often intervene 

 between the inner edges of the inferomarginal plates. The whole of 

 the dorsal surface is rough with spines ; the pore-areas are, on the 

 back, very distinct, and generally triangular ; they are specially large 

 along the sides of the arms, the pores large ; the granulation is rather 

 coarse and the granules reach very nearly to the tip of the spines 

 and spinous tubercles. Madreporic plate large, irregular in shape. 



Measurements: — R = 117; r=48 ; greatest breadth of arm 3-5. 



Colour, brownish (in alcohol). 



Hab. Billiton. 



