448 



THE VOYAGE OF H.M.S. CHALLENGER. 



and forming a semicircular scoop-like fan. (2.) An obliquely placed flat comb of four 

 spinelets, similar in size and character to those on the actinal intermediate plates and 

 appressed to the ray. 



Mouth-plates very large, with a prominent superficial actinal keel. Marginal armature 

 forming three fans : an inner or buccal one common to the two plates, and a lateral one 

 on each plate. On the median keel is a short lineal series of small conical spines on each 

 plate. 



Madreporiform body small, suboval, situated near the margin, marked with numerous 

 very fine strise. 



Anal aperture excentric, inconspicuous. 



No pedicellarise of any kind are present. 



Arhbulacral tube-feet with a fleshy terminal disk, centrally invaginated, forming two 

 regular series. 



Remarks. — This large and well-marked form resembles Crossaster very closely when 

 seen from above. It may be distinguished, however, at once by the structure of the 

 actinal surface, the armature of the adambulacral plates, the presence and armature of the 

 actinal intermediate plates, the character of the armature of the marginal plates, and the 

 structure of the mouth-plates : a congeries of characters which furnish the generic features 

 of Rhipidaster. 



Clwrology of the Genus Rhipidaster 



a. Geographical distribution : — 



Eastern Archipelago : One species between the parallels of 5° and 15° S. 



Rhipidaster vannipes, in the Arafura Sea, between Cape York 

 and Frederick Henry Island. 



/3. Bath y metrical range : 28 fathoms. 

 7. Nature of the Sea-bottom : Green mud. 



Chorological Synopisis of the Species. 



1. Rhipndaster vannipes, n. sp. (PI. LXIX. figs. 1-4). 



Kays eight. E = 85 to 88 mm. ; r=27 mm. E<3 r. Breadth of a ray at the base, 

 about 18 mm. 



Disk large, the general habit resembling that of Crossaster papposus. Rays rather 



