350 TIIE VOYAGE OF H.M.S. CHALLENGER. 



at about one-third of the distance from the centre to the margin. Its surface is covered 

 with numerous and very fine striae, and the margin is raised, which gives the organ a 

 " put-on " appearance. 



The ambulacral tube-feet are very large, and have large fleshy sucker disks. 



Colour in alcohol, a bleached yellowish white. 



Locality. — Station 187. Booby Island, Torres Strait. September 9, 1874. Lat. 

 10° 36' 0" S., long. 141° 55' 0" E. Depth 6 fathoms. Coral mud. Surface temperature 

 77° 7 Fahr. 



Remarks. — This species shows affinities to Pentaceros ivestermanni and the group 

 of forms allied to Pentaceros orientalis. Pentaceros callimorphus differs conspicuously 

 from these, as well as from other members of the genus, by the character of the armature 

 of the adambulacral plates (see foregoing description) ; and by the spinulation of the 

 actinal intermediate plates, — the lineal arrangement of spinelets on the rows of inter- 

 mediate plates external to the adambulacral plates on each side of the furrow imparting 

 a very striking ornamentation to the actinal surface. The character and the uniformity 

 of the size of the tubercles on the abactiual surface, as well as the large, regular, and 

 well-defined papular areas, are also noteworthy. 



Genus Pentaceropsis, n. gen. 



All recent writers who have discussed the structural characters of Pentaceros 

 obtusatus (Bory de Saint Vincent), Perrier, have thrown out the suggestion that its 

 peculiarities demand generic recognition, but no one has been bold enough to actually 

 place it apart. In taking this step now, I fear that I may incur the risk of drawing 

 upon myself the stigma implied by the poet as merited by those whose footsteps are less 

 timorous than those of more gifted persons ! Having no desire to be accredited with wings 

 at the expense of my convictions, I propose to call the genus Pentaceropsis, as indicating 

 its affinity to Pentaceros. It is characterised by the generally flat form, by the presence 

 of the intercalated series of plates between the supero-marginal and infero-marginal plates 

 in the interbrachial arcs, and by the irregular character of the abactinal plating. 



Ghorology of the Genus Pentaceropsis. 

 a. Geographical distribution : — 



Eastern Archipelago and (?) Indian Ocean : One species between the parallels 

 of 20° N. and 30° S. 



Pentaceropsis obtusatus, from the Philippine Islands, and also 

 reputed to have been found at Mauritius. The latter locality appears 

 to be doubtful. 

 /3. Bathymetrical range : Shallow water. 

 •y. Nature of the Sea-bottom : Not recorded. 



