94 s. goto: 



ai'ea iu œntro of disk (iucluding the ceutriil cone) aud ou five naiTOw radial 

 and five naiTOW iuterradial areas extending from the contre like the spokes of 

 a Avlieel. On either side of the radial areas, papiilcX) extend to tip of ray. 



" Marginal plates. — Superomarginal plates exactly opposite inferomar- 

 ginals. The former are thin and confined to side Avail of ray. The actino- 

 lateral border of ray with its series of spines is slightly nearer upper than 

 lower border of iuferomarginals. The part of inferomarginal below the 

 actinolateral spine has a rather broad speciahsed ridge, which is broader 

 tlian intervening fasciolar fmTow. Tliis fm-row is roofed over by a single row 

 of spinelets immersed in a continuous web, eight or nine of these sx^inelets 

 occmTing between lower edge of plate and actinolateral spine. When dried 

 the sm'face of plate shows often numerous minute bosses. Directly above 

 the actinolateral spine the specialised ridge narrows abruptly and joins without 

 a conspicuous break, that of superomarginal. The fasciolar channel is several 

 times broader than the specialised ridge and is a V-shai)ed trough, on whose 

 sides are five to seven parallel superimposed but distinctly spaced series of 

 delicate spinelets in a continuous web. Each web extends from the upper 

 end of a superomarginal plate to the actinolateral spine. The wliole apx)aratus 

 (^f five to seven webs or himellœ on either side of the V-shai)ed trough, 

 extending over its cavity, forms a veiy delicate cribriform organ or filter. 

 The series of spinelets roofing the fmi'ow are much flattened and the tip 

 ends in several minute jwints. Owing to the greater width of fm-row, these 

 spinelets are much longer than those of lower end of iuferomarginals. The 

 other spinelets are narrow and more delicate and decrease in size in each 

 successive tier toward bottom of fm-row. In alcoholic specimens the mem- 

 brane investing the spinelets is usually so tliick tliat they are only seen with 

 difficulty. The si)inelets act only as a sui3j)ort for the membrane and do not 

 themselves function as strainers, as in Astrqpeden. The superomarginal spine 

 which stands at the top of the plate is either terete, tapering, and pointed, 

 or broadly lanceolate and acute like a spear tip. On outer part of ray there 

 are sometimes two spines on a few i)lates. 



" Tlie variation iu number of marginal platas has already been indicated 

 in the table. The margin of ray and disk is thicker in some examples than 



