92 - PTERASTERIDAE. 



which are clothed, distally at least, with thick opaque skin; the middle spiaes 

 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 

 sUghtly convex lobe well-supported by the actinolateral spines 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 points. Adambulacral armature 

 consists of a single, acicular spine, about 3 mm. long and not at aU sacculate. 

 Aperture papillae nearly sessile, rounded triangular, not as wide as high and 

 scarcely one tliird 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 beU 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 Ufe, the tube-feet on the proximal half of the rays 

 wovild 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 

 imnatural 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 



