REPOBT ON THE ASTEROIDEA. G25 



and at a right angle to the direction of the ray. The spine is delicate and tapering, 

 covered with membrane, and a few pedicellariae are usually congregated near the distal 

 extremity. On the middle of the plate one large spine stands perpendicularly ; it measures 

 5 to 6 mm. in length, and is encased in a membranous sheath crowded with pedicellariae. 

 The pedicellariae are similar to those previously noticed, and measure from 0'175 to 0"2 mm. 

 in length on a spine near the base of the ray. On the inner portion of the ray, extending 

 perhaps half way along the ovarial swelling, these spines are flaring and flattened at the 

 tip, with a truncate extremity coarsely crenulate, and the membranous sheath is not con- 

 tinued over this expanded portion, but terminates abruptly in a roll at its commencement. 

 The flattened extremity is trausverse to the direction of the ray. Beyond the ovarial 

 region the spine is delicate, tapering, and sharply pointed, and the membrane has a 

 saccular prolongation. The long lateral spines which fringe the margin of the rays do not 

 occur on every plate, but usually on alternate ones ; sometimes, however, two unarmed 

 plates are together, and rarely two succeeding plates bear a lateral spine. The spines, 

 which are of great length and delicacy, measure from 14 to 19 mm. near the middle of 

 the ray, are articulated on a rudimentary infero-marginal plate ankylosed to the outer 

 margin of the adambulacral plate, and are enveloped in a delicate membranous sheath 

 crowded with pedicellariae, which develops a saccular prolongation at the distal extremity. 

 Very few lateral spines are present on the ovarial region, and only on the outer part. The 

 spines here are short (about 4 mm.), and with their membrane appear more robust ; they 

 increase in length as they proceed outward, and again diminish at the extremity of the ray. 

 The pedicellariae are attached to the membrane by long thread-like stalks, and the valves 

 when closed measure 0"11 mm. on a spine 12 mm. long, from near the middle of the ray. 

 The thickness of the spinelet, just above its widely expanded articulatory base, is only 

 0-177 mm. 



The actinostome is large and of wide expanse, as in all the group; its diameter is 14'5 

 mm. in a disk of 20 mm. diameter. Within its periphery, and at a higher level, is a broad 

 tract of delicate buccal membrane surrounding the widely open mouth. The membrane is 

 semitransparent, and the internal organs are more or less clearly visible through it ; the 

 margin is strongly muscular, and has a subvillous or papillose appearance. 



The mouth-plates are small and quite inconspicuous, and the median suture line is in- 

 discernible. The adoral margin of the united pair in each "mouth-angle" is semicircular, 

 and four small mouth-spines are borne upon it, two on each plate. The inner spine on 

 each plate stands close to the median line of juncture, forming a pair nearly parallel to one 

 another and directed horizontally towards the centre of the mouth. The other mouth- 

 spine on each plate is also directed horizontally, but at an angle of about 45° to the direc- 

 tion of the inner spine. The marginal mouth-spines are short (2 mm. in length), and are 

 covered with a thin membranous sac, slightly expanded midway between the extremities, 

 which gives a subfusiform appearance to the spinelet, and a few isolated pedicellariae are 



(ZOOL. CHALL. EXP. — PART LI. — 1888.) 79 



