82 PROF. F. J. BKLL ON THE [Feb. 1 9j 



outer is thicker than the inner. The ventral plates each bear a 

 spine; the ambulacral spinulation is triplacanthid. R=200 miUim. 

 Hab. Sumatra. 



Oreaster gracilis. 



Oreaster gracilis, Liitken, Vidensk. Medd. 1871, p. 260. 



As there is in the British Museum collection a specimen the 

 spread of which must exceed the largest of Dr. Liitken's specimens 

 by more than .50 millim., it may be convenient to give an account 

 of it. 



11 = 2-87 r. Disk not elevated; arms narrov? at their base, 

 slender in proportion to the disk ; lophial line well marked, but not 

 projecting ; the apical spines of moderate height, and a smaller 

 central spine. 



About 30 superomarginal and in feromarginal plates ; the greater 

 number of these are large, and both sets take part in forming the 

 sides of the arm. In the angles of the arm they are elongated from 

 above downwards ; further out the upper are longest in the direction 

 of the long axis of the arm, while the lower are squarish. In the 

 specimen under description the two inferomarginals in the angle 

 of the arm are always, and the corresponding superomarginals are 

 sometimes, provided with bluntly conical spinous projections ; incon- 

 spicuous tubercular projections are developed ou a few of the quite 

 distal superomarginal plates. 



Adambulacral spinulation triplacanthid ; in the innermost row 

 ordinarily nine rather delicate spines, of which the median are the 

 longest : the middle and outer rows have generally two spines each ; 

 these are stouter than the inner spines, and those of the median are 

 a little stronger than those of the outer row. The ventral plates 

 are quite distinct from one another, the covering granulation being 

 so arranged that each ossicle seems to have its proper investment ; 

 on the actinal surface of the disk these ossicles seem to have no 

 definite arrangement ; along the greater part of the arm there runs 

 but a single row of ossicles between the ambulacrum and the infero- 

 marginal plates ; these ventral ossicles are all of the same size, and 

 the larger may be often seen to have pushed their way into the 

 slight space between two succeeding inferomarginal plates. Fair- 

 sized pedicellariae are developed on some of the ossicles that lie 

 nearest to the adambulacral plates. 



The marginal plates are very regularly granulated, and appear to be 

 altogether devoid of pedicellarise. The granulation on the upper 

 surface is still more delicate ; the general appearance of this aspect 

 of the disk is well stated in the words of Liitken, " Dorsum disci 

 regulariter reticulatum, areis poriferis trigonis, nodis trabecularum 

 tuberculiferis ; " but of this specimen it is hardly correct to add 

 " tuberculis minutis." 



In the face of the fact that this is a larger specimen than either 

 examined by Dr. Liitken, and that the tubercles at the nodal points 

 of the reticulating ossicles are, so far as one can judge, better de- 

 veloped than in his specimens, the question arises as to the extent 



