1100 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
Supradorsal membrane thick, soft, fleshy, and nearly opaque in alcohol. It is irregularly 
wrinkled, very probably due to shrinkage in alcohol, and in consistency resembles the bell of a tough 
jellyfish. Scattered rather widely along the radial areas are a number of prominent, soft, pointed 
papillae. In the type these are almost wanting, or are at least very short, but in 2 other specimens, 
which undoubtedly belong to this species, they attain the length of about 8 mm. Their size depends 
somewhat upon the degree of contraction of the dorsal membrane surrounding them. There are 
about 30 to 40 to each radius, in the specimen on which they are best developed, and 2 or 3 stand in 
the interradius near the oscular valves. Each has a very slender paxilla spinelet running its whole 
length. From the outside these paxilla spinelets are scarcely perceptible, as they are exceedingly 
delicate. If the actinolateral membrane is carefully removed they may be seen springing from the 
very rudimentary abactinal membrane or true body wall. Each paxilla consists of a slender, cylin- 
drical, basal portion, the summit of which is slightly enlarged to afford articulation for 4 extremely 
delicate, long, bristle-like spinelets united by membrane, -which enter the supradorsal membrane and 
radiate widely apart, imbedded in the tissue. Occasionally there are 5 in the larger fascicles on the 
lateral and proximal portions of the radial areas. It is one of these slender spinelets which is 
imbedded in the papilla and extends to its tip. Not all the paxillar fascicles have papillae corre- 
sponding to them. The paxilhe are well-spaced and extend in 2 irregular series along each side of the 
median radial line, those of the outer series being largest. All diminish in size toward extremity of 
area. No specialized bands of muscle in the supradorsal membrane. Spiracula microscopic, very' 
inconspicuous and impossible to detect without strong magnification; confined to small, elongated, 
irregular, or substellate groups, of 25 or even more, which are widely scattered among the papillae. 
Oscular orifice large. Valves broad, nearly truncate, fan-shaped, all united by a web. Spines slender, 
numerous (18-19), about 10 or 11 mm. long, springing from a fan-shaped, triangular basal piece, with 
a curved margin (about 6 mm. wide) for the attachment of spines. 
Ambulacral furrow wide (8-12 mm.) , narrowing abruptly toward extremity; shallow. Armature 
consists of 2 slender, tapering, sharp spinules close together in a longitudinal, often a trifle oblique 
series, on tumid furrow margin. Adoral spinule is slightly the longer, although near base of ray it 
may be shorter. Both are sheathed in membrane, which is not evident except at tip, where there is a 
sort of fleshy thickening, extending slightly beyond extremity. Distal plates of series (usually 
beyond middle) have only 1 spine. Rarely a few scattered plates in proximal portion of series have 
but 1, also, and the first plate usually 3. Segmental apertures small; aperture papilla (the spinule 
standing directly in front of each aperture and acting as a valve to close it) of fairly large size, rather 
broadly suboval, invested with a pulpy membrane. Aperture papilla of the first adambulacral plate 
is multifid, and is immersed in the actinolateral membrane, for which it acts as a sort of support, 
immediately behind the combined mouth plates. 
Mouth plates large and broad, with a prominent keel at the interradial junction of the plates. 
The outer end of the combined pair is most prominent, forming a sharp point which projects upward 
when the specimen is laid on its back. The inner end also forms a beak pointed toward the actino- 
stome. Armature consists of a marginal series of 5 sharp, slender spinules on the lateral flange. 
Rarely a sixth spinule is added adjacent to the first adambulacral. A membrane-invested spinelet 
similar to and homologous with the aperture papillae stands just external to the innermost of the 
marginal spinelets. Rarely an acicular spinelet stands on the general surface of the lateral flange. 
Actinolateral spines long, slender, and rather closely placed, about 40 to 50 in number. 
Actinolateral membrane translucent. 
M^dreporic body, as seen through the dorsal osculum, is large and very convex. 
Color in life, light rose pink. 
Localities: Type (no. 21185, U. S. National Museum) from station 4090, northeast approach to 
Pailolo Channel, between Maui and Molokai islands, 304-308 fathoms, fine gray sand; bottom temp. 
43.8°. Taken also at 3911, south coast of Oahu, 337-334 fathoms, fine gray sand and mud; 3914, 
289-292 fathoms, gray sand. and mud, same locality (6 specimens). 
This species is characterized by the shape of the disk, the generally fleshy character of the 
supradorsal integument, by the miscroscopic spiracula, and by the armature of the adambulacral and 
mouth plates. It most nearly resembles Hymenaster carnosus Sladen, from off the west coast of South 
America (1,500 fathoms), from- which it differs in the number and distribution of spiracula, character 
of abactinal surface, shape of disk, armature of adambulacral and mouth plates, and probably also in 
having weaker paxillse spinelets. 
