526 THE VOYAGE OF H.M.S. CHALLENGER. 
Genus Benthaster, Sladen. 
Benthaster, Sladen, Journ. Linn. Soc. Lond. (Zool.), 1882, vol. xvi. p. 242. 
Form depressed. Marginal contour stellato-pentagonoid. Abactinal area convex. 
Actinal area plane. 
Supradorsal canopy rudimentary. No muscular fibrous bands. No spiracula. Nida- 
mental cavity more or less aborted. Paxillee with subfascicular crowns; spinelets tri- 
laminate, of extraordinary length, delicacy, and number, protruding the greater portion 
of their length naked beyond the supradorsal membrane. Paxille probably devoid of 
investing membrane. Papule simple, globular, sessile sacs, comparatively large. Special 
dorso-lateral (? supero-marginal) plates at the extremities of the rays. Ossicles of the 
abactinal surface cruciform, greatly attenuated, the whole calcareous framework being 
reduced to a minimum. 
Adambulacral armature consisting of one or two spinelets, which are long, needle- 
shaped, independent, and not united by membrane. Aperture-papille more or less 
modified. Segmental apertures (?) aborted. 
Mouth-plates of the Hymenaster type. ‘Two pairs of secondary or superficial mouth- 
spines, robust, clavate, thorny, probably without saccular membrane. Mouth-spines proper 
two or three, the innermost resembling the anterior pair of secondaries, only rather 
smaller, the others pointed. 
Actino-lateral spines merged in the actinal floor. 
Remarks.—The superficial aspect of this genus recalls, to a certain extent, that of 
Korethraster, from which, however, it is structurally widely separate. The rudimentary 
supradorsal membrane, and the long, fasciculated, naked, paxillar spinelets, protruding 
far beyond the membrane, readily distinguish the genus from Hymenaster ; whilst the 
simple independent armature of the adambulacral plates, not forming combs and not 
webbed, at once distinguishes Benthaster from Marsipaster, the only other form with 
which it can be compared. 
Chorology of the Genus Benthaster. 
a. Geographical distribution :— 
Paciric: Two species between the parallels of 40° N. and 10 8. 
Benthaster wyville-thomsoni, from the Mid-North Pacific, near the 
meridian of 170° E. Benthaster penicillatus, off the north coast of 
New Guinea, south-west of the Admiralty Islands. 
B. Bathymetrical range: 1070 to 2900 fathoms. 
y. Nature of the Sea-bottom: Benthaster wyville-thomsoni on Red clay ; Benthaster 
penicillatus on Blue mud. 
