440 



THE VOYAGE OF H.M.S. CHALLENGER. 



Supero-marginal plates large. Infero-marginal plates small, each with one small, 

 compressed, horizontally disposed lateral spine, forming a regular longitudinal series at the 

 ambital margin. Papulae single, isolated, forming regular longitudinal lines between 

 the plates. 



Adambulacral plates small, contingent on the infero-marginal plates, not separated 

 by papulae. Adambulacral armature consisting of two equal spines which form two 

 regular longitudinal rows. 



Adambulacral tube-feet quadriserial in arrangement, with a fleshy, button-like, 

 centrally invaginated terminal disk. 



Madreporiform body small, occupying the median area of a basal plate near the 

 margin. 



Anal aperture present, excentric, external to the dorso-central plate. 



Chorology of the Genus Tarsaster. 

 a. Geographical distribution : — 



Pacific : One species between the parallels of 10° N. and 10° S. 



Tarsaster stoichocles, off D'Entrecasteaux Reef, North of Ad- 

 miralty Islands. 



/?. Bathymetrical range : 150 fathoms. 



y. Nature of the Sea-bottom : Coral mud. 



Cliorological Synopsis of the Species. 



1. Tarsaster stoichocles, n. sp. (PI. CIV. figs. 5-8). 



Rays five. R = 53 mm. ; r = 5 mm. R > 10 r. Breadth of ray at the base, 675 mm. 



Rays elongate, rather broad at the base in relation to the small disk, subcylindrical, 

 convex, and arched abactinally, tapering from the base to the extremity, slightly con- 

 stricted at the base. Disk very small, slightly convex, not higher than the base of the 

 rays, the junction of the rays and disk being defined by a depression. 



The abactinal area is beset with relatively large plates. The disk is covered with the 

 primary apical plates, very few others being present, jj The plates upon the rays are 



