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



rounded margin of the ray and is directed outward at an angle of about 45° to the plane 

 of the abactinal surface. The surface of the plate is entirely covered with small, equal, 

 papilliform granules, or minute stunted clavate spinelets ; and occasionally one or two 

 immediately below the conical spine are longer, more definitely spine-like, and tapering. 



The infero-marginal plates alternate with the superior series, and both their height and 

 their breadth are greater than their length. Each plate bears a short, robust, conical but 

 often truncate lateral spine, which is, however, longer and 'more robust than the spine 

 on the supero-marginal plates ; and this is followed by two or three, or even more, smaller 

 tapering and pointed spinelets ; the character of the whole spinulation along the median 

 part of the plate being definitely spine-like, the spinelets decreasing in size as they recede 

 from the lateral spine and approach the inner end of the plate; two or sometimes 

 three irregular series may be frequently defined, one series, however, being larger than 

 the others. The rest of the surface of the plate is covered with small papilliform 

 spinelets, which become more crowded, delicate, and cilia-like along the margins of the 

 transverse sutures. 



The adambulacral plates are broad and form prominent angular projections into the 

 furrow. Their armature consists of : — (1.) A furrow series of six or seven rather elongate 

 spinelets, rather robust at the base, tapering and sharply pointed ; the median spinelet is 

 the longest, and all radiate apart. (2.) On the surface of the plate is an obliquely trans- 

 verse series of two or three robust conical spinelets, rather longer than any of the furrow 

 series, the outer one being longest when two are present, and the middle one when there 

 are three ; on each side of these are two or three small spinelets near the margins of the 

 plate. 



The mouth-plates are large, convex, and subtubercular ; and their surface is covered 

 with short, conical, pointed spinelets, which decrease slightly in size as they recede from 

 the mouth, but no definite order of disposition can be made out, and the mouth-plates 

 have consequently a remarkably echinulate appearance. The true mouth-spines consist 

 of a marginal series of about nine tapering, pointed spinelets on each plate, the two inner- 

 most being fully twice as long and robust as the others, and slightly compressed. There 

 are thus four powerful mouth-spines at each angle guarding the actinostome ; and two or 

 three of the superficial spines immediately behind these are equally robust. 



The actinal interradial areas are of very small dimensions, and the intermediate or 

 ventral plates are few in number and do not extend beyond the fourth or fifth adam- 

 bulacral plate. The separate plates are indistinguishable in spirit specimens, and their 

 surface is covered with small, conical, and pointed spinelets. 



The anal aperture is central and distinct, often surrounded by larger spinelets. 



The madreporiform body is large, oval, and slightly convex, the inner end of the plate 

 being about midway between the centre of the disk and the margin. Its surface is 

 furrowed with numerous fine and deeply cut striations ; many sharply bent and con- 



