484 THE VOYAGE OF H.M.S. CHALLENGER. 
Supradorsal membrane an irregularly developed, somewhat spongiform, tissue. No 
muscular fibrous bands. No spicules. Paxillee with moderately expanded crowns com- 
posed of a great number of fine, long, hair-like spinelets (fifteen to thirty), their extremities 
protruding freely through the membrane. Paxille invested with a well-developed mem- 
branous envelope. 
Adambulacral armature forming transverse combs, consisting of spines webbed 
together ; the spinelets more or less horizontal in position, overspanning the furrow. 
Mouth-plates with one secondary or superficial spine on the actinal surface, connected 
with the mouth-spine series by a continuation of the web. Mouth-spines proper three on 
each plate, webbed together. 
Actino-lateral spines merged in the actinal floor ; no independent marginal fringe. 
Remarks.—This genus is nearly related to Pteraster,—from which, however, it is dis- 
tinguished by the rudimentary character of the supradorsal membrane, devoid of muscular 
fibrous bands; by the actino-lateral spines being merged in the actinal floor; and by the 
absence of a marginal fringe. Furthermore, the numerous hair-like spinelets of the paxillze 
protruding through the supradorsal membrane give a peculiar character to the abactinal 
area ; and the spines which constitute the armature of the adambulacral plates, from their 
high position in the furrow and from their more or less horizontal direction, present a 
feature unknown in the other members of the group. 
The representatives of this genus collected by the Challenger are all from the Pacific ; 
the occurrence of an Atlantic species is, however, reported by Perrier’ in a summary of 
the novelties obtained by the “ Talisman ” Expedition, but no description has yet been 
published, and the position of the dredging station is not stated. 
Chorology of the Genus Marsipaster. 
a. Geographical distribution :— 
AtLantic: One species between the parallels of 10° and 50° N. 
Marsipaster alveolatus, dredged by the “Talisman” Expedition. 
Paciric: Two species between the parallels of 30° and 40° S. 
Marsipaster spinosissimus, in the Mid-South Pacific, near the 
meridian of 185° W. Marsipaster hirsutus, between Valparaiso 
and the Island of Juan Fernandez. 
8. Bathymetrical range: 2160 to 2335 fathoms. 
y. Nature of the Sea-bottom: Marsipaster spinosissimus on Red clay ; Marsipaster 
hirsutus on Blue mud. 
} Ann. Sci. Nut. (Zool.), 1885, 6e Série, t. xix. Art. No. 8, p. 69. 
