198 BULLETIN 70, UNITED STATES NATIONAL MUSEUM. 



MEDIASTER ^Q0ALIS Stimpson. 



ri. 35, figs. 1-3; pi. 5!), figs. 1, la-c. 



Mediasler xqualis Stimpson, Boston Journ. Nat. Hist., vol. 6, 1857, p. 530, pi. 23, figs. 7-11.— 

 J. F. WniTEAVES, Trans. Roy. Soc. Canada, vol. 4, sec. 4, 1886 (1887), p. 117 (Malcolm Island, 

 Queen Charlotte Sound, British Columbia). — Sladen, Challenger Asteroidea, 1889, p. 572.— 

 Vekrill, Trans. Conn. Acad., vol. 10, 1899, p. 179, pi. 24, figs. 10-12. 



Description. — Ray.s five. R° = 84 mm.; r = 32 mm.; R = 2.6r. Breadth of ray 

 at base, 36 mm. R'' = 56 mm.; r = 22 mm.; R = 1.54 r. Breadth of ray at base, 

 26 mm. Interbrachial arcs wide, rounded or subangular; rays regularly tapering, 

 rather slender toward tip, blunt. Marginal plates conspicuous, but as a rule not 

 encroaching much on abactinal area; sides of body rather evenly rounded. 

 Superomarginals, twenty-eight to a ray (in a specimen with R = 84 mm.), almost 

 plane to slightly tumid, wider than long, covered with many small pentagonal to 

 roundish, close set, but nevertheless distinctly spaced, flat-topped granules, of which 

 the marginal series is larger, and transversely oblong; a plate here and there may 

 bear a typical low bivalved podicellaria with two or three jaws, these not extending 

 above the level of the granulation, but with a base four or five times as wide as 

 height of jaw. Inferomarginals similar to superomarginals, the suture between 

 the two series being more or less zigzag. 



Abactinal surface usually slightl}' convex, covered with large tabulate plates or 

 parapaxillie well spaced as a rule, and bearing a flat-topped ornate crown of up- 

 wards to twenty-four central, trapeziform, pentagonal, or more rarely roundish, 

 truncate or convex slightly spaced granules, and upwards to 25 slightly longer 

 peripheral granules, with an upper face four-sided and beveled inward; frequentl}' 

 some of the granules are replaced by a large low bivalved pedicellaria; median 

 radial row of plates attain the terminal plate and the adradials frequently, but not 

 always. Papular areas extensive; papulfe two or three in a cluster, about six 

 clusters around a plate; lacking at tip of ray and from a small triangular interradial 

 area near margin; abactinal plates roundish, with six short lobes, well spaced 

 (except off the papular regions), and connected by small independent internal 

 radiating ossicles, six to a plate. 



Actinal interradial areas extensive, the intermediate plates extending nearly 

 to tip of ray; they are close set, broadly ovate, slightly imbricated and bear roundish, 

 rhombic, or elliptical groups of two or three central (also one or none) and five to 

 ten peripheral prismatic, elongated or spiniform granules. A few plates especially 

 near furrow, bear a good-sized bivalved pedicellaria with two, three, or four jaws, 

 sometimes higher and not so long at the base, as abactinal pedicellariae. 



Adambulacral plates squarish, not large, with a furrow series of three to five, 

 oblong, more or less prismatic or compressed blunt spinelets, subequal in size; external 

 to these, two successively shorter series form a rosette-like group, those nearest 

 the furrow series being thicker than the latter, prismatic, or quadrate in section 

 and about three in number; the outermost series usually has four or five granules 

 like those of adjacent intermediate plates; occasionally on the outer half of ray an 

 adoral spinelct of the inner series is replaced by a pedicellaria with two or three 



" Example from Albatross station 4228— S. E. Alaska. 



f> Example from Albatross station 3159— off Point Reyes, California. 



