356 BULLETIN" 100, UNITED STATES NATIONAL MUSEUM. 



What appear to be the superomarginal plates are 2 in number 

 (omitting the large distal plate) and are relatively widely separated 

 from the inferomarginals (3 mm.), being actually abactinal in posi- 

 tion, and the outer is at the proximal third of ray. They are covered 

 by 4 or 5 tubercles (one larger than the rest) and a circle of tumid 

 granules. 



In A. tuherculosus the 3 superomarginals are relatively less spaced 

 from the inferomarginals and have a conspicuous bare surface. In 

 elegans the superomarginals and the tubercular intermarginal plates 

 may bear a pedicellaria. The terminal superomarginal is broadly 

 oval, less convex, and larger than in tuber culosiis^ its long diam- 

 eter being 5.5 mm. or about one-fourth the length of ray meas- 

 ured on side. Inferomarginals 9, decreasing regularly in size, cov- 

 ered with coarse granules, with usually a tubercle on the margin. 

 The proximal 4 or 5 are separated by 1 or 2 vertical series of plates. 

 They are about equal in size to the superomarginals, whereas in A. 

 tuherculosus the inferomarginals are conspicuously the smaller, and 

 moreover bear a large acorn-shaped tubercle occupying all or nearly 

 all the surface of plate. 



The actinal intermediate plates bear 5 to 10 very coarse unequal, 

 convex or tubercular granules, 1 of which is enlarged into a hemi- 

 spherical or low acorn-shaped tubercle, 1 or 2 of the granules being 

 only slightly smaller. These tubercles are most prominent on the 

 outer half of ray, and near the mouth plates, being smaller inter- 

 radially. Many of the plates bear a curved slender 2- jawed 

 pedicellaria. 



Furrow spines 4, slightly compressed, round-tipped, the adoral 

 slightly shorter than the other 3. Subambulacral spines 2, heavy, 

 round-tipped, in a transverse series, the outer the shorter. The mar- 

 gin of plate is provided with a series of small pinched granules. 

 Marginal mouth spines 8 ; suboral spines usually 3 in a series parallel 

 to furrow. 



The differences between this species and A. tuherculosus may be 

 summed up as follows: tubereulosus differs from elegans in having 

 numerous small granules between the abactinal tubercles, and sur- 

 rounding not only the primary tubercles, but also the secondary; 

 these granules are smaller and more beadlike; the superomarginal 

 plates are conspicuously larger than the inferomarginal (not sub- 

 equal), are lateral in position (not abactinal), and are situated nearer 

 to the inferomarginals; they are mostly naked and surrounded by 

 a series of beadlike granules; the inferomarginals, instead of being 

 covered by numerous coarse gi-anules (as in elegans), are provided 

 with an acorn-shaped tubercle occupying all the surface of the plate ; 

 the terminal superomarginal is more convex and smaller ; in elegans 

 the actinal intermediate granules or tubercles of each plate are 



