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 tothe 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 striz. 
Anal aperture excentric, inconspicuous. 
No pedicellarize of any kind are present. 
Ambulacral 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. 
Chorology of the Genus Rhipidaster 
a. Geographical distribution :— 
EastERN ARCHIPELAGO : One species between the parallels of 5° and 15° 8. 
Rhipidaster vannipes, in the Arafura Sea, between Cape York 
and Frederick Henry Island. 
8. Bathymetrical range: 28 fathoms. 
y. Nature of the Sea-bottom: Green mud. 
Chorological Synopsis of the Species. 
Ocean. | Range in Fathoms. Nature of the Sea-bottom. | 
| 
Rhipiduster vannipes . . | Eastern Archipelago. | 28 Green mud. | 
1. Rhipidaster vannipes, n. sp. (P]. LXIX. figs. 1-4). 
Rays eight. R=85 to 88 mm.; r=27 mm. R<3~7r. Breadth of a ray at the base, 
about 18 mm. 
Disk large, the general habit resembling that of Crossaster papposus. Rays rather 
