532 THE VOYAGE OF H.M.S. CHALLENGER. 



1. Pyihonaster murrayi, n. sp. (PL XCV. figs. 1-5). 



Kays five. R= 150 mm. ; r = 17 mm. R < 9 r. Breadth of a ray at the base, 19 

 mm. ; breadth at 19 mm. from the base, 9 mm. ; midway between the centre and the 

 extremity, 5 '5 mm. 



Rays very elongate, flexible, narrow, subcylindrical, subcarinate and compressed 

 laterally on the outer part, considerably swollen and inflated at the base but rapidly 

 becoming slender at a short distance from the disk ; they then appear to maintain a 

 nearly uniform breadth for some distance along the ray, and finally taper gradually to an 

 attenuate extremity. 



A transverse section of the ray, midway between the centre and the extremity, would 

 present an outline nearly resembling that of a gothic arch, with the apex slightly rounded, 

 the vertical height bein<r greater than the breadth. The lateral walls terminate with an 

 abrupt rounding upon the actinal surface, this rounding being occupied entirely by the 

 adambulacral plates ; nearly the whole of the actinal surface of the ray is thus taken up 

 by the ambulacral furrow. 



The disk is small, and its real size is so much masked that the starfish has the appear- 

 ance of being composed of five united rays only, the deception being produced by the 

 presence of a deep sulcus or channel, which traverses each interradial line. This constric- 

 tion emphasises the swelling at the base of the ray, and also causes the ray to appear to 

 be continued nearly to the centre of the disk. In the central area there is some depres- 

 sion, in the midst of which is located a well-developed valvular apparatus similar to 

 that closing the oscular orifice in the Pterasteridse. This consists of five triangular 

 fan-like valves, radial in position, each composed of delicate spinelets united by mem- 

 brane, which meet together when shut down and completely close the dorso-central 

 aperture. 



The abactinal and lateral areas are beset with extremely delicate plates, which are 

 imbedded in membrane and are invisible without microscopic preparation. The orna- 

 mentation of these surfaces presents a very remarkable appearance. It consists of short, 

 minute spinelets, grouped together into fasciculi, five to ten in each, borne on the plates 

 above mentioned ; and each fasciculus is enclosed in a membranous sac, which causes them 

 to appear like little semiglobular bags only. Under magnification the extremities of 

 spinelets may here and there be seen protruding through the membrane, and the inter- 

 spaces are also covered with membrane. The fasciculi are arranged with great regularity 

 in oblicmely transverse fines on each side of the median radial line, and pass along the deep 

 lateral wall of the ray up to the adambulacral plates. In the median portion of the radial 

 areas of the disk and along the median line of the ray, the sacculi are smaller and are dis- 

 posed without order and consequently independent of the transverse series. This irregular 

 median band is very narrow along the ray, but expands towards the base and on the radial 

 area of the disk. The rows run nearly parallel to the interradial line, and maintain the 



