110 THE VOYAGE OF H.M.S. CHALLENGER. 
Synopsis of the Species included in the Genus Pseudarchaster herein described. 
A. With incipient post-adambulacral fascioles 5 : 5 : . ; 3 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 ‘ : : E 5 : , intermedius. 
Chorology of the Genus Pseudarchaster. 
a, Geographical distribution :— 
Artantic : Two species between the parallels of 50° N. and 40° 8. 
Pseudarchaster intermedius off the coast of North America, south 
of Nova Scotia. Pseudarchaster tessellatus off the Cape of Good 
Hope. 
Pacrric : One species between the parallels of 40° and 50° 8. 
Pseudarchaster discus in the Messier Channel, between the 
western coast of South America and Wellington Island. 
8. Bathymetrical range: Shallow water to 147 fathoms. 
All the known species are thus confined to the littoral zone. 
y. Nature of the Sea-bottom: Pseudarchaster intermedius on gravel and stones. 
Pseudarchaster discus on Blue mud. Pseudarchaster tessellatus in shallow 
water (?) Simon’s Bay. 
Chorological Synopsis of the Species. 
Ocean. | Range in Fathoms. Nature of the Sea-bottom. | 
i | | 
Pseudarchaster discus. . | Pacific. 147 Blue mud. 
Pseudarchaster intermedius . | Atlantic. 49 | Gravel and Stones. 
Pseudarchaster tessellatus . : | Atlantic. | Shallow water (?) _ Shallow water (2) 
| | 
1. Pseudarchaster discus, n. sp. (Pl. XIX. figs. 1 and 2; Pl. XLII. figs. 3 and 4). 
Rays five R=30mm.;r=12mm. R=2571. 
Rays rather short, broad at the base and tapering gradually towards the extremity, 
breadth midway between the centre of the disk and the extremity, 65 mm. Interbra- 
chial arcs wide and well rounded. 
