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



5. Rhopalastrum ypsilinum, n. sp. (PI. 43, fig. 2). 



Distance between the paired arms half as large as their distance from the odd arm. All three 

 arms at the concavely curved distal end three times as broad as at the narrow base. Odd arm 

 twice as long and broad as the paired arms. Central disk smaller than the latter. No terminal 

 spines. 



Dimensions. Radius of the odd arm O32, of the paired arms 02 ; terminal breadth of the 

 former 0'2, of the latter 012. 



Habitat. Indian Ocean, Cocos Islands, Rabbe, surface. 



6. Rhopalastrum clavatum, n. sp. 



Distance between the paired arms half as large as their distance from the odd arm. All three 

 arms club-shaped, at the thickened, nearly spherical, distal end three times as broad as at the 

 narrow base. Odd arm nearly twice as long and broad as the paired arms. Central disk equal 

 to the distal knob of the latter. No terminal spines. 



Dimensions. Radius of the odd arm 0'3, of the paired arms 0'18 ; distal breadth of the former 

 016, of the latter 008. 



Habitat. South Atlantic, Station 332, surface. 



7. Rhopalastrum irregulare, n. sp. (PL 43, fig. 8). 



Distance between all three arm-points different. All three arms cylindrical, nearly of the same 

 length, but of different form, irregularly curved, about four times as long as broad, with blunt 

 ends. 



Dimensions. Length of each arm about 0'2, breadth 0'05. 



Habitat. Antarctic Sea, Station 157, depth 1950 fathoms. 



Subgenus 2. Rhopalastromma, Haeckel. 

 Definition. Arms on the distal end provided with one or more terminal spines. 



8. Rhopalastrum martellum, n. sp. 



Distance between all three arm-points nearly the same ; but the odd arm is one and a half times 

 as large as both paired arms, and is perpendicular to the common axis of the latter, therefore the 

 shell has the form of a hammer. Each arm is twice as broad at the distal end as at the base, 

 and armed with a conical terminal spine ; the latter is vertical in the odd arm, horizontal in the 

 paired arms. 



Dimensions. Radius of the odd arm 0'3, of the paired arms 015 ; distal breadth of the former 

 012, of the latter 0'06. 



Habitat. North Atlantic, Station 354, surface. 



