134 



THE VOYAGE OF H.M.S. CHALLENGER. 



Eastern Archipelago : One species between the parallels of 0° and 10° S. 



Porcellanaster caulifer in the Arafura Sea, between AustraHa 

 and New Guinea. 



(3. Bathymetrical range: 800 fathoms to 2550 fathoms. 



All the species are confined to the Abyssal zone, and one only (Porcellanaster 

 caulifer) is found at a less depth than 1000 fathoms. Three species, Porcella- 

 naster crassus, Porcellanaster gracilis, and Porcellanaster eremicus are found 

 in depths greater than 2000 fathoms. 



Porcellanaster cseruleus is the only species known to me from more than one 

 locality, and its range is very constant, varying only from 1240 to 1350 fathoms. 



y. Nature of the Sea-bottom : Three species are found on the Blue mud, viz. : 



Porcellanaster cseruleus in the Atlantic, and Porcellanaster gracilis and 

 Porcellanaster tuberosus in the Pacific. Porcellanaster crassus and Porcel- 

 lanaster eremicus are found on the Eed clay in the Pacific and South Atlantic 

 respectively. Porcellanaster caulifer lives on Green mud in 800 fathoms. 



Chorological Synopsis of the Species. 



1. Porcellanaster cseruleus, Wyville Thomson (PI. XX. figs. 1-7). 



Porcellanaster ceruleus, Wyville Thomson, 1877, Voy. of Challenger, Atlantic, vol. i. p. 378, figs. 

 97 and 98. 



Pays five. R = 22 mm.; r = 10'5 mm. (the largest example). R = 2 r, approxi- 

 mately. 



Marginal contour substellate, with moderately developed rays proceeding from a 

 truly pentagonal body-disk, the minor radius being in the proportion of 48-50 per cent. 

 When viewed from above the rays seem comparatively small and have the appearance 

 of springing somewhat rapidly from the angles of the disk, the interbrachial arc being 

 very wide and not unfrequently quite straight, or even curved outward, rather than 

 rounded. Disk more or less gibbous and inflated, the height being sometimes equal to 

 one-third of the greatest diameter, but generally less. The arching or inflation of the 



