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



Genus Pholidaster, Sladen. 

 Pholidaster, Sladen in Narr. ChalL Exp., 1885, vol. i., p. 616. 



Disk small. Rays long, tapering, subcylindrieal and flexible. Interbrachial arcs acute. 



Abactinal plates arranged in regular longitudinal series (the median radial series 

 largest), bearing large plate-like skin-covered scales, which mask all the plates except 

 some of the primary apical plates on the disk and the median radial series along the ray. 

 Small isolated papulae are present at the angles of the plates. 



Supero-marginal plates subequal in size to the median radial series of plates, and 

 bearing plate-like skin-covered scales similar to those above described. Infero-marginal 

 plates smaller than the superior series and bearing a single, delicate, elongate, naked lateral 

 spine appressed to the ray, and several compressed, scale-like, skin-covered spinelets. 



Actinal intermediate plates two or three series, each plate bearing a single naked 

 spinelet similar to the lateral spine, appressed to the ray, and several skin-covered papillae ; 

 the large spines forming longitudinal series along the ray. 



Adambulacral plates broader than long, each alternate plate with a prominent ridge 

 which extends far into the furrow, the intermediate plates appearing to form the straight 

 wall of the furrow. Adambulacral armature consisting of a pair of delicate furrow spines, 

 which radiate apart at the inner end of the ridge ; on the outer part of the plate is a group 

 of skin-covered papillae parallel to the furrow. The intermediate non-prominent adam- 

 bulacral plates only bear the group of skin-covered papillae, and a few more prominent 

 extending to the margin of the furrow. 



Madreporiform body more or less masked by the plate-like scales of the abactinal 

 plates ; the striations appear to be few in number and coarse. 



Anal aperture inconspicuous and excentric ; closed by squamiform plates. 



No pedicellariae present. 



Ambulacral tube-feet with a terminal fleshy knob ; crowded and forming four alter- 

 nating rows. 



Remarks. — This genus is unquestionably related to Zoroaster, of which it is probably 

 the shallow-water representative in this tropical area. Pholidaster is, however, readily 

 distinguished from Zoroaster and from all other known forms by the presence of the 

 remarkable scales borne on the abactinal and marginal plates. So far as at present known 

 the genus has a very small area of distribution. 



Chorology of the Genus Pholidaster. 

 a. Geographical distribution: — 



Eastern Archipelago : Two species between the parallels of 20° N. and 10° S. 

 Pholidaster squamatus off the Philippine Islands. Pholidaster dis- 

 tinctus in the Banda Sea, between the Ki Islands and the Banda Islands. 



