203 THE VOYAGE OF H.M.S. CHALLENGER. 



regular transverse rows, about five in each. The larger paxillse have a circlet of ten to 

 twelve short spinelets surrounding a rather large tabulum, on which one to three low 

 granules are placed ; and the smaller ones have about eight, with one central. The 

 paxilloe are smaller and very compact in the centre of the disk, and a prominent conical 

 peak is present. 



The supero-marginal plates, which are twenty-two or twenty-three in number from 

 the median interradial line to the extremity, are slightly broader than long : their height 

 is greater than the length, and increases on the inner portion of the ray, where it is greater 

 than the breadth. The plates are slightly tumid and well-defined ; and are covered with 

 low rounded granules, which are larger and more prominent on the middle of the plate. 

 Normally each plate bears a prominent spiniform granule on the rounding that unites the 

 abactinal and lateral surfaces ; and occasionally a second may be present close beside it. 

 Usually one or two of the innermost plates on each side of the median interradial line 

 carry two of these spiniform granules, of equal size. 



The infero-marginal plates do not protrude beyond the line of the superior series, and 

 are gently rounded towards the actinal area. Each plate has a single, short, slightly 

 compressed, and sharply taperiDg lateral spine, followed by two similar but shorter 

 spinelets, placed close behind, and forming a line slightly oblique to the median line of 

 breadth of the plate. The second spine is about two-thirds the length of the lateral spine, 

 and the third is much le ss and more compressed. This triplet of spines is confined to the 

 marginal edge of the plate, and no other spines are present, except on one or two of the 

 innermost plates, the rest of the plate being covered with small uniform squamules, and 

 these, though short, are more or less spatuliform and have rounded tips. 



Only two or three actinal intermediate plates are present, and these bear small, uuiform, 

 papilliform spinelets. 



The armature of the adambulacral plates consists of short spines, which normally form 

 two series ; but on some plates the outer series is somewhat irregular, and the arrange- 

 ment may simulate the appearance of three series. The inner or furrow series consists of 

 three spines, of which the middle one is longest, straight, cylindrical and tapering ; whilst 

 the two lateral ones are short, delicate, compressed in the direction of the axis of the ray, 

 slightly expanding towards the tip, and truncately rounded. The outer series consists of 

 three spines, equal in size, broad, robust, flatly compressed in the direction of the axis of 

 the ray, widely flaring towards the extremity, and truncate. The middle spinelet is 

 on some plates placed external to the two lateral ones, and sometimes in consequence 

 appears like a solitary spinelet of a third series. Sometimes also the aboral lateral 

 spinelet may be slightly in advance. On a few of the innermost plates one or two 

 supplementary spinelets may be present. 



The mouth-plates are large and prominent, with a single line of short, robust, papilli- 

 form spinelets upon the surface of the keel, along each side of the median suture ; these 



