ECniNODERMATA — CLARK. 537 



OPHIURA CTENOPHORA,i« sp.nov. 



(Plate li, figs. 4-6). 



Diameter of disc, 13 miu.; lengtli of arm, 33 mm. Disc high, 

 slightly convex, covered by about 100-150 plates, among which 

 the central dorsal, five radial, five interradial, five interradial 

 marginal, and ten ladial shields are easily distinguishable. 

 Radial shields broad at outer end, but longer than wide, more 

 or less separated proximally by two or three small plates ; in 

 young specimens they are in contact distally, but in some old ones 

 they are separated for their entire length. Upper arm-plates in 

 contact on basal part of arm, but on outer half or third of arm 

 are well sepKrated ; first upper arm-plate very broadly triangular, 

 but apparently oblong, slightly swollen, seemingly longer than 

 broad, entirely contained between upper ends of genital plates, 

 which conceal much of it ; second plate very short, two or three 

 times as wide as long ; third plate also two or three times 

 times as wide as long, but with a more or less convex outer 

 margin ; fourth plate more or less hexagonal, much wider than 

 long, fifth plate (in adults) also hexagonal, but nearly as long as 

 wide ; sixth and following (sometimes as far as thirteenth) plates 

 similar, but inner end becoming nari'ower ; succeeding plates 

 triangular, with a sharp proximal angle and a convex outer 

 margin, becoming very minute at tip of arm. Upper ends of 

 genital plates conspicuous on each side of arm, at base, rounded, 

 very slightl}' swollen, as wide as or wider than first upper arm- 

 plate ; a supplementary genital plate lies between the ventral end 

 of the genital plate and the oral shield ; arm-comb begins on 

 supplementary genital, and following edge of genital, passes up 

 on to outer end of radial shield ; it consists of about 30-35 

 papillae, which are ventrally small and bead-like, but becoming 

 broad and flat, they are gradually more and more elongated, and 

 appear, dorsally, as slender spinelets, which are longest on upper 

 •em! of genital plates; a conspicuous supplementary arm-comb of 

 very small spinelets is developed on each side of basal upper arm- 

 plate. Interbrachial spaces below, covered by the huge oral shields 

 and supplementary genital plates ; a few marginal plates are 

 barely visible. Oral shields much longer than wide, with a blunt 

 angle inward. Adoral plates longer than wide, narrower at outer 

 •end than at inner. Oral plates conspicuous, neai'ly or quite as 

 large as adorals, often with a third transverse plate at tip of jaw. 

 Oral papillge three or four on each side, outermost widest ; an 

 infradental papilla at apex of jaw. First under-arm plate much 



^"/(■reis, /crfi/d?=comb -|- ^opeoa^to bear or carry, in reference to ttie 

 highly developed arm-comb. 



