REPORT ON THE ASTEROIDEA. . 529 



2. Benthaster periicillatus, Sladen (PI. XCIV. figs. 6-9). 



Bcntlia?t<r jirnirillatu!,, Sladen, 1882, Journ. Linn. Soc. Lond. (Zool.), vol. xvi. p. 245. 



Marginal contour stellato-pentagonoicl ; interbrachial arcs moderately indented and 

 well rounded. Minor radial proportion 65 - 2 per cent. R= 11*5 mm. ; r = 7'5 mm. The 

 rays taper gradually, and their extremities are somewhat upturned. 



The supradorsal membrane is exceedingly delicate and rudimentary, appearing little 

 more than a thin mucous film over the interradial areas, becoming, however, rather 

 spongiform over the rays. The pedicles of the paxillae are very thin and delicate, bearing 

 a crown of extremely long, thin, needle-like spines, seven or eight times the length of the 

 pedicle ; there are about twenty spinelets in a crown on the disk, and about half that 

 number, or less, towards the extremities of the rays. The spinelets are of the most delicate 

 description, vitreous in appearance, trilaminate, the transverse section representing three 

 cylindrical rods placed together, instead of three flattened laminae, as in the preceding 

 species. The spinelets are widened at their proximal extremity into a condyloid articula- 

 tory base, all fitting close together, and each moulded to the form of its fellows, the whole 

 forming a compact basement to the crown. The spinelets constituting a crown expand 

 very slightly apart, and protrude the greater portion of their length free and naked 

 through the supradorsal membrane. 



The cruciform ossicles of the abactinal surface, upon which the paxillae are borne, are 

 very delicate, the prolongations being attenuated to a remarkable degree, here and there 

 almost aborted, and the central portion of the ossicle manifesting a tendency to become 

 rotund and squamiform. This modification is so far carried out, that in the centre of 

 the disk the whole of the abactinal surface that can be seen under the oscular orifice is 

 simply covered with subcircular scales. 



The oscular orifice is very large. The valves (or their representatives) consist of a 

 compressed paxilla-crown composed of rather more robust spinelets than the rest. The 

 pedicles of these modified paxilhe are very much enlarged, compressed laterally, and 

 expanded at the top, upon which the spinelets are articulated in a more or less regular 

 double row, the pedicles standing in the median radial line. Powerful muscular bands 

 run between the bases of the pedicles of the valves and form a regular pentagon, near the 

 centre of which the anal aperture is situated. Close to the periproct and less than 

 its own breadth away is the remarkably small, round, insignificant, madreporiform body. 

 The papula? are simple round sacs, as broad as long, and immensely large in proportion to 

 the pedicles by which they stand. 



Supero-marginal plates are present at the extremity of the ray, and form a terminal 

 arch or ocular guard ; but they are not half the length of the similar pieces in the pre- 

 ceding species. 



The ambulacral furrows are wide, not petaloid, and the margins of the furrow are 

 very narrow. The armature of the adambulacral plates consists of two or three spines 



(zool. chall. exp. — part li. — 18S8.) 67 



