92 PTERASTERIDAE. 
which are clothed, distally at least, with thick opaque skin; the middle spies 
are about twice as long as the most lateral. In each interradius is a notch about 
a millimeter deep, on each side of which the interbrachial membrane forms a 
slightly convex lobe well-supported by the actinolateral spmes whose distal 
ends are covered with thick opaque skin. The triangular interbrachial area is 
about 10 mm. deep (along the interradius) and in its present contracted condi- 
tion about 6-8 mm. wide along the free margin. Actinolateral spines about 
fifteen, of which the third or fourth seems to be the longest; the thick skin in 
which the spines are somewhat imbedded and the shape and condition of the 
specimen prevent exact determination of these pomts. Adambulacral armature 
consists of a single, acicular spine, about 3 mm. long and not at all sacculate. 
Aperture papillae nearly sessile, rounded triangular, not as wide as high and 
scarcely one third the length of the adambulacral spine. Oral plates fused to 
form a jaw whose length, breadth, and height (distally) are about equal; the 
slope from the distal end of the keel to the inner tip of the jaw is exceptionally 
steep; the breadth of the whole jaw, distally is probably considerably more 
than the height but this is hard to determine; on the outer distal corner of each 
oral plate are two slender oral spines 1.5—2 mm. long and just below the middle 
of the surface of each plate is a suboral spine about 3 mm. long and very similar 
to the adambulacral spines; none of these spines is at all sacculate. Color of 
supradorsal membrane dull bluish except where it is thickened over the tips of 
spinelets and spines; in such places it is yellowish white; oral surface nearly 
black except the interbrachial membrane between the tips of the rays which is 
contrastingly yellowish white. 
Station 4658. Eastern Tropical Pacific, 8° 30’ S., 85° 35’ 36” W., 2,370 fms. Bott. temp. 35.3°. Fne, 
gn. m., mang. nod. 
One specimen. 
It is difficult to determine how much of the extraordinary bell-shape of 
this curious Hymenaster is due to contraction caused by its capture and preserva- 
tion. The bell is much deeper and narrower than in Koehler’s campanulatus 
and the rays do not project noticeably beyond its margin. If this were the 
normal form of the animal in life, the tube-feet on the proximal half of the rays 
would be useless; indeed progression would have to be by swimming freely in 
the water. It is very probable that the form of the preserved specimen is quite 
unnatural and is due to extreme contraction of the interbrachial areas especially 
along their margins. The armature of the adambulacral and oral plates is very 
distinctive and the coloration is also peculiar, the heavy pigmentation of the 
