148 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



and from these the odd series, containing 4 plates, reaches about half- 

 way to the marginal plates. The intermediate plates have a convex 

 ridge, not very high, bearing numerous lanceolate appressed squami- 

 form spinelets, increasing in size toward the furrow. 



Adambulacral armature : Furrow spines 8 or 9 (7 far along ray) 

 rectangular in section, compressed,, bluntly pointed, lanceolate in 

 contour, the edge to furrow. The median 2 or 3 spines are a little 

 longer than the base line of the series; the others are increasingly 

 shorter toward either end of series. Subambulacral spines 25 to 30. 

 Four to 6 slender, tapering, somewhat flattened, sharp spines, about 

 two-thirds as long as the furrow spines, form a regular series just 

 back of the furrow series. The remaining spinelets are much shorter 

 and form 2 or 3 irregular longitudinal series, with several spinelets 

 out of line, or there may be no definite arrangement. 



The denuded mouth plates have a narrower inner end than in D. 

 nesiotes^ which has the actinostomial angle of the combined plates 

 broad and rounded, very much as in D. grandissimus (Goto, 1914, 

 pi. 8, fig. 137). The margin bearing the oral spines is longer than in 

 nesiotes and gi^andissiTnus ^ especially in proportion to the edge ad- 

 jacent to first adambulacral, while the angle formed by the posterior 

 ends of the two plates is wider and extends farther inward than in 

 either of the two forms mentioned. (See pi. 41, fig. la.) 



Marginal mouth spines 10, similar to those of the adambulacral 

 plates, but heavier toward the inner end. The convex surface is be- 

 set with numerous short, thick, granuliform spinelets, increasing 

 in length at the inner end of the plates. Two or 3 flattened granuli- 

 form spinelets form a very simple pedicellarian apparatus over 

 the median suture, near outer end of the plates. 



Madreporic body large, 12 mm. in diameter, situated 14 mm. 

 from inner margin of superomarginal plates and concealed by about 

 25 large paxillae standing on its surface. 



Type.— C^i. No. 37037, U.S.N.M. 



Type-locality. — Station 5115, Verde Island Passage, north coast 

 of Mindoro, 340 fathoms. 



Distribution. — Known only from the type-locality. 



Remarks. — Dipsacaster imperialis is related rather closely to four 

 species — D. nesiotes., D. sladeni^ D. grandissiiiviLS^ and D. laetino- 

 philus.^ The nearest relative seems to be D. nesiotes., although I have 

 not been able to make comparisons directly with specimens of 

 D. grandissimus. The squarish superomarginals characterize sla- 

 deni, nesiotes, imperialis, and laetmophilus, while grandissimus 



1 Alcock, 1893, p. 87, pi. 5, figs. 3 and 4 ; Andaman Sea, 250 fathoms. 



2 Goto, 1914, p. 252, pi. 8, figs. 136-139; pi. 9, figs. 140-1-11; o£f Misaki, .Japan, 840 

 meters. 



8 Fisher, IQlld, p. 95, pi. 12, fig. 3 ; pi. 15, figs. 1, 2 ; pi. 52, figs. 3, 3a, 3& ; pi. 53, 

 fig. 2; south of Alaska Peninsula, 695 fathoms. 



J 



