550 THE VOYAGE OF H.M.S. CHALLENGER. 



29° 55' 0" S., long. 178° 14' 0" W. Depth 520 fathoms. Volcanic mud. Bottom tem- 

 perature 43 o- Fahr. ; surface temperature 65° - Fahr. 



Remarks. — Whether the inflation at the base of the ray is the normal form, or is due 

 to this specimen being a female and in a gravid condition, I am unable to say without 

 mutilating the single example at my disposal. The species may be recognised by its 

 general form, by the character of the spinulation of the abactinal plates, and by the struc- 

 ture of the lateral and actinal skeleton. 



Genus Perknaster, n. gen. 



Disk large and more or less inflated. Rays cylindrical and tapering. 



Abactinal and lateral surfaces up to the adambulacral plates covered with small 

 undistinguishable plates, which bear groups of short, equal spinelets, covered with skin, 

 dispersed in tufts or paxilliform groups, more or less compactly placed. 



Armature of the adambulacral plates disposed in one or two transverse series ; the 

 innermost spinelet usually large and thickly skin-covered. No small inner spinelet placed 

 high up in the furrow as in Cribrdla. 



Madreporiform body distinct, situated about midway between the centre of the disk 

 aud the margin ; surface marked with fine, convoluted striations. 



Anal aperture subcentral and inconspicuous. 



Ambulacral tube-feet in regular biserial arrangement, and having large fleshy ter- 

 minal disks. 



No pedicellarise of any kind present. 



Remarks. — This genus, though allied to Cribrdla, is at once characterised by the 

 large development of the disk, by the compact structure of the abactinal and lateral 

 skeleton, by the homogeneity of the marginal plates, and by the character of the 

 armature of the adambulacral plates. The general facies of the forms I have included 

 in the genus is very different from that of Cribrdla, or any other type. 



Chorology of the Gams Perknaster. 



a. Geographical distribution : — 



Southern Ocean : Two species between the parallels of 45" and 55° S. 



Perknaster ■ fuscus and Perknaster densus, from Kerguelen 

 Island, the former also from Heard Island. 



/?. Bathymetrical range: 25 fathoms to 127 fathoms. 



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



