108 Mr. A. Alcock on 



the small plates on each side of this prominent mid-radial 

 row ; and (iii.) by the paucity of pedicellariai, even the spines 

 of the adambulacral plates being oftener without these organs 

 than with them. 



In the young stage (R = 6"5r) the apical and abactinal 

 raid-radial plates are extremely prominent, the tip of the rays 

 is capped by a large, inflated, spiny terminal plate, and the 

 tube-feet are but indistinctly quadriserial. 



42. Zoroaster Gilesii^ sp. n. 

 Rays 5. R = about 8 r. R = 70 millim. 



Disk comparatively large, low, flat or very gently convex, 

 very distinctly delimited from the rays (above which it is not 

 much elevated) by a complete ring of massive semiglobular 

 plates ; abactinally it is encased in concentric series of these 

 great semiglobular plates (with or without small sunken 

 plates intervening) in the following order : — a dorso-central, 

 five basal interradials, five primary radials (the largest of all), 

 and twenty-five marginal plates, of which one succeeds each 

 primary radial and four close in each interradial area. All 

 the plates are covered with capillary spinelets with a few 

 coarser spinelets interspersed, and the intervals between the 

 plates are occupied by papulte and rather numerous large 

 pedicellaria3. 



The rays are rigid, broadish, and flat, with a gentle abac- 

 tinal convexity, and are encased in thirteen longitudinal 

 parallel series of small and very close-set tumid plates, which 

 also stand in obliquely transverse parallel series. These 

 plates have the following arrangement : — (i.) a mid-radial 

 row of suboctagonal slightly imbricating plates lying in a 

 furrow between two rows of distant papulae (which two rows 

 of papula3 are the only papulae present on the rays), flanked 

 on each side by (ii.) six rows of very close-set bead-like 

 plates, of which the upper (abaci inad) three rows are much 

 the larger, the lower (actinad) three rows consisting of minute 

 plates so crowded together as to appear at first sight like a 

 single row. All these plates are covered with coarse spinelets, 

 which are larger and denser in the three lower (actinad) rows, 

 and those of the mid- radial and three upper (abactinad) rows 

 on each side have also a small coarse spine centrally, and on 

 each suture margin a largish pedicellaria, while those of the 

 three lower rows have each a long lanceolate spine. 



Adambulacral plates small and short, but extending high 

 up into the furrow ; each plate has two transversely placed 



