1 LO 



THE VOYAGE OF II.M.S. CHALLENGER. 



Synopsis of the Sjiecies included in the Genus Pseudarchaster herein described. 



A. With incipient post-adambulacral fascioles discus. 



B. With no trace of incipient post-adambulacral fascioles. 



a. With small distinct isolated spinelets on the infero-marginal plates ; and one 



prominent spinelet on the actinal surface of the adambulacral plates . tessellatus. 



b. Without specialised isolated spines intermedins. 



Chorology of the Genus Pseudarchaster. 

 «. Geographical distribution : — 



Atlantic : Two species between the parallels of 50° N. and 40° S. 



Pseudarchaster intermedins off the coast of North America, south 

 of Nova Scotia. Pseudarchaster tessellatus off the Cape of Good 

 Hope. 



Pacific : One species between the parallels of 40° and 50° S. 



Pseudarchaster discus in the Messier Channel, between the 

 western coast of South America and Wellington Island. 



(3. Bathy metrical range: Shallow water to 147 fathoms. 



All the known species are thus confined to the littoral zone. 



y. Nature of the Sea-bottom: Pseudarchaster intermedins on gravel and stones. 

 Pseudarchaster discus on Blue mud. Pseudarchaster tessellatus in shallow 

 water (?) Simon's Bay. 



Chorological Synopsis of the Species. 



1. Pseudarchaster discus, n. sp. (PI. XIX. figs. 1 and 2 ; PI. XLII. figs. 3 and 4). 



Rays five. R = 30 mm. ; r = 12 mm. R = 2"5 r. 



Rays rather short, broad at the base and tapering gradually towards the extremity, 

 breadth midway between the centre of the disk and the extremity, 6 "5 mm. Interbra- 

 chial arcs wide and well rounded. 



