92 BULLETIN 76, UNITED STATES NATIONAL MUSEUM 



scries there is sometimes one zigzag scries, or two, or the space may be filled with 

 spines aol regularly arranged. Those of disk form small groups, or stand singly, 

 liii i arc not typically acervate. 



The papular areas arc in more or less distinguishable longiseries abactinally. 

 Those occupying the Bupramarginal channel form a fairly straight row. Two others 

 between this series and the carinal plates can be made out in some specimens- 

 six for the abactinal area (Petropavlovsk, Kuril Islands). In two specimens from 

 Medni, Commander Islands, the central area of ray is broken up and irregular. 

 One series of intermarginal areas; proximally two series and distally one of actinal. 

 Areas small, two to fivo papulae each. 



Superomarginal spines two, capitate, striate, sometimes a trifle larger than the 

 dorsals, forming a regular duplicate longiseries rather high on side of ray, with the 

 conspicuous supramarginal channel above and an intermarginal channel below. 

 A specimen from Petropavlovsk has an arcuate vertical series of three spines on 

 most of the plates. The marginal series of plates bend upward at the base of the 

 ray, and the upper series of spines, which border the abactinal surface, passes inward 

 on the interradial line, adjacent to the same series of the neighboring ray. 



The inferomarginal spines are usually one to a plate proximally and two dis- 

 tally. They are cylindrical, or slightly clavate, round-tipped, and are distinctly 

 heavier and longer than the superomarginals on the proximal half of the ray, but 

 only a trifle larger distally, where the lower of the two spines is sometimes longer 

 than the upper. In this case the upper is subequal to the superomarginals. There 

 are two series of actinal spines (and two series of plates), the outer extending three- 

 fourths to nearly the whole length of the ray, while the inner reaches to the middle 

 in large specimens (B 47 mm.). 



The first five to eight adambulacral plates carry a single, slender, rather long, 

 terete slightly tapered blunt spine, followed by a very variable number (usually 

 few) which have mostly two spines. Then the plates have one and two spines 

 in fairly regular alternation; or less often mostly one spine with diplacanthid plates 

 irregularly scattered. Beyond the first half dozen adoral plates the spines become 

 shorter and thicker, often clavate, with the exception of the alternate furrow spine 

 of diplacanthid plates, which is generally decidedly slenderer than the others. It 

 is, however, frequently of the same clavate, or club-shaped, form as the others. 

 The first three pairs of adoral adambulacral plates are in contact interradially ; 

 the lirst two plates are longer than the succeeding plates by about 30 to 50 per 



eelit. 



Mouth plates very similar to those of alaskensis and typically there are three 

 spines, two at the inner apex and one at the actinal surface. Sometimes the shorter 

 of the apical spines, which corresponds to the furrow spine of diplacanthid adambul- 

 acral plates, is lacking. The longer, that adjacent to median suture, is about as 

 long as this suture, or a little shorter. The two spines of a pair are frequently dis- 

 similar in length. The suboral is slender, tapering, and upwards of twice the length 

 of the apical spine. 



Straight pediccllariae (pi. 42 fig. lc) inconspicuous and few abactinally, outside the 

 supramarginal channels. They are broadly lanceolate to ovate, sharp to blunt, and 

 measure 0.36-0.46 mm. They are very inconsiderable in size as compared to the 



