REPOET ON THE ASTEROIDEA. 447 



The actinal intcrradial areas of the disk are covered with membrane, beneath which 

 may be detected traces of small intermediate plates ; and on only one or two of these is 

 there a single short stumpy spine. 



The madreporiform body is small, circular, convex, and situated about midway between 

 the centre of the disk and the margin. 



The ambulacral tube-feet have a large, fleshy, centrally invaginated terminal disk. 



Colour in alcohol, a dirty brownish white. 



Young Phase (?).— There is a very small example of a Crossaster from Station 145, 

 which I am inclined to think may be the young of this species, but the specimen is too 

 small for accurate determination, measuring only R = 7'5nirn. There are ten rays. In 

 the armature of the adambulacral plates there are two or three spinelets in the furrow 

 series, and four or five in the transverse series. 



Localities. — Station 135o. Off Nightingale Island, Tristan da Cunha. October 17, 

 1873. Lat. 37° 25' 30" S., long. 12° 28' 30" W. Depth 110 fathoms. Surface tem- 

 perature 54 o- Fahr. 



? Station 145. Off Marion Island. December 27, 1873. Lat. 46' 43' 0" S., long. 

 38° 4' 30" E. Depth 140 fathoms. Volcanic sand. Surface temperature 41° - Fahr. 



Remarks. — This species resembles Crossaster papposus in habit, but is distinguished 

 from that form by the number of rays, which are also narrower and more attenuate, by 

 the widely spaced marginal combs, by the smaller paxillse on the abactinal surface, which 

 are more widely spaced and have fewer and more elongate spinelets in the crown, by the 

 distinctly rounded interbrachial arcs, and by the skin-covered actinal interradial areas 

 devoid of spinelets, as well as by the character of the armature of the adambulacral plates. 



Genus Rkipidaster, n. gen. 



Disk large, slightly convex, general form depressed, the habit resembling that of 

 Crossaster. Eays (eight in the type form) robust and tapering. 



Abactinal plates forming a wide-meshed reticulated network, bearing isolated paxilli- 

 form tufts of spinelets. Several large isolated papulae are present in the meshes ; and 

 the membrane of the interspaces is beset with round, granule-like, fleshy papillae round the 

 margin of the papular orifice, and groups of the same are present on the membrane. 



A series of marginal plates (? supero-marginal) which bear paxilliform tufts of rather 

 elongate spines appressed to the ray, defines the abactinal area. 



A single complete longitudinal series of actinal intermediate (or perhaps the repre- 

 sentatives of infero-marginal) plates is present between the supero-marginal and adam- 

 bulacral plates, each plate bearing a flat fan of spines appressed to the ray. 



Adambulacral plates large. Armature consisting of two series of spines. (1.) The 

 furrow series of seven or eight delicate spines partially united by a membranous web, 



