220 BULLETIN 76, UNITED STATES NATIONAL MUSEUM. 



ginals in contact medially, terminal plate larjije, ovoid, usually separating the last 

 suporomarginals of either side. All abactinal plates with very strongly stellate 

 bases, and all with stout, low tabula bearing, as a rule four to twelve large over- 

 hanging, crowded triangular, qiuidrate, or pentagonal marginal granules, fre- 

 quently surrounding one to three smaller polygonal granules; often no central 

 granules; the crown of granules circular or more often irregularly polygonal and 

 resembling, with tabula, a miniature toadstool; primary apical plates, and also 

 sometimes others in center of disk, with numerous central granules. Actinal in- 

 termediate ])lates with unequal, large triangular, trapeziform, square and polyg- 

 onal, very slightly spaced nearly flat-topped granules; plates quadrate with usually 

 a rhomboidal form. Adambulacral plates short and wnde, transversely oblong in 

 form, with a furrow series of usually two, less commonly .three, short swollen, blunt, 

 frequently compressed upright spinelets, which do not extend much if any above 

 the general surface of the actinal granulation. Actinal surface with three to six 

 granules, one of which immediately behind the furrow series is larger than rest; 

 frequently an upright bivalved pedicellaria with oblong, truncate or round-tipped 

 jaws stands among the granules, above wliich it does not extend. 



Description. — The abactinal paxilliform plates are very characteristic in their 

 armature. The granules are slightly convex, and the marginal series overhang so 

 that from the side a paxilla has the form of a miniature toadstool. The granules 

 are large, few in number, and frequently the central granules are lacking. Sui>er- 

 ficially the tabula bear a great resemblance to Sladen's figure of Gnathaster elonga- 

 tus.'^ The outer or free edge of the granules is straight, curved, or angular. The 

 primary basal ])lates have much smaller and numerous granules so that they are 

 conspicuous among the other plates. In a specimen from the Shumagm Islands 

 a curious coalescence of the granules has taken place on some of the tabula. In 

 one case all but two, in another all but three, and in still another aU the granules 

 have fused, leaving no sutures. The latter looks like a nail head. The plates are 

 in fairly regular series parallel with the median radial. No abactinal pedicellariae. 



The papulfe seem to be generally distributed except for a narrow line where 

 the interradial septum meets the abactinal wall. The plates have strongly stellate 

 bases, the development of the lobes being on the side toward the median radial line. 

 Thus most of the plates have two or tlu'ee lobes only, which impinge ui)on two or 

 three neighboring plates, as shown by the figures. The great extent of the papular 

 area causes all the plates to have these lobes, which sometimes show sutures at 

 their base, as if on the road to form an independent ossicle. 



Superomarginal plates eighteen to twenty-four to a side; inferomarginals, two 

 more. The superomarginals are nearly square in the interbrachial arc, the width 

 being slightly greater than length ; distally the width greatly exceeds the length. A 

 little over half the exposed surface is usually bare, except in a large specimen from 

 Bering Island, in which the distal plates have a small bare spot. A single series 

 of large, squarish, close-set granules borders the inner and lateral edges of the bare 

 area, the outer portion of the plate being closely set with large rhomboid, trapezi- 

 form, and jjolygonal granules, those nearest the outer edge being the largest. The 

 inferomarginals are similar to the superomarginals, but the bare spot is smaller. 



« Challenger Asteroidea, pi. 49, fifr. 5- 



