644 THE VOYAGE OF II.M.S. CHALLENGER. 



the plate is somewhat broader than the aboral, and the margin towards the furrow is 

 rather deeply concave, the greatest depth lying between the median point of the furrow 

 margin aud its aboral extremity, where the plate stretches prominently into the furrow, 

 forming a well-defined bay along which the ambulacral tube-foot passes, and by which 

 it is separated from the succeeding tube-foot. The armature of the adambulacral plates 

 consists of: — (1.) a small spinelet attached to the aboral prominence of the plate above- 

 mentioned, and directed horizontally over the furrow and at a slight angle in the direction 

 of the ray ; (2.) a longer spine standing perpendicularly and articulated on a tubercular 

 elevation on the middle of the actinal surface of the plate; and (3.) a lateral spine on 

 alternate plates articulated on a tubercle-like rudimentary infero-marginal plate anky- 

 losed on the lateral margin of the adambulacral plate. The small inner spinelet 

 is rather more than a millimetre in length, and comparatively robust at the base ; it is 

 often flattened and expanded at the tip, which is truncate and subspatulate, the whole 

 covered with membrane bearing a rather numerous congregation of pedicellarise. The 

 perpendicular spine is delicate and tapering ; the longest are about 5 mm. in length, but 

 at 80 or 90 mm. from the disk they are not more than 2 to 3 mm., and their length 

 generally appears to be rather irregular ; they are encased in a membranous sheath, with 

 a more or less elongate saccular prolongation, and the wdiole is covered with crowded pedi- 

 cellariae. On the ovarial region the distal extremity of these spines is usually expanded 

 like the proximal articulatory base, and is truncate, which gives them a robust clavate 

 appearance. The lateral spines are of great delicacy; the longest measure 16 to 18 mm., 

 and they are encased in a sheath of very delicate membrane with crowded pedicellarise, 

 and there is a comparatively large saccular knob at the extremity. The pedicellarise are 

 exceedingly small and attached to the membrane by long thread-like stalks. Unfor- 

 tunately, very few of these spinelets are to be found unbroken, owing to the extreme 

 fragility and delicacy of the specimen, and probably also to the difficulty in detaching 

 it from the hempen tangles. It is much shattered, and I am therefore unable to say with 

 accuracy what the general habit of the ray would be in comparison with that of other 

 species, but I am disposed to think that the lateral spines were relatively short in pro- 

 portion to the great length of the rays, and that they were certainly more delicate than 

 usual. 



The actinostome is large and wide, its diameter being about 12 mm., in a disk mea- 

 suring 19 mm. The buccal membrane is of great delicacy, and semitransparent. The 

 mouth-plates are small and inconspicuous, and present a remarkably straight margin 

 towards the actinostome. Two small mouth-spines are borne on each plate, of a pecu- 

 liarly curved, semicrescentic or semiscimitar form ; they have the appearance of bending 

 round until the outward prolongation of the distal extremity is at a right angle to the 

 prolongation of the median line of the mouth-plates, and their shortness gives them the 

 appearance of being turned back so as to fit almost close to the margin of the plate. They 



