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



5. Rhoiyalastrum yj^silinum, 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 ternrhial 

 spines. 



DiTnensions. — Eadius of the odd arm 0-32, of the paired arms 0-2 ; terminal breadth of the 

 former 0-2, of the latter 012. 



Habitat. — Indian Ocean, Cocos Islands, Eabbe, surface. 



6. Rhopalastrum clavatum, n. s^. 



Distance between the pau-ed 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 

 nan-ow 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. — Eadius of the odd arm 0-3, of the paired arms 0'18 ; distal breadth of the former 

 0-16, of the latter 0-08. 



Habitat. — South Atlantic, Station 332, surface. 



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



Distance Ijetween all three arm-points different. All three arms cylmdrical, 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. RJioixdastromma, Haeckel. 

 Definition. — Arms on the distal end pro"saded \\dth one or more terminal spines. 



8. Rhopalastrum martellum, u. sp. 



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

 as large as lioth 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. — Eadius of the odd arm 0'3, of the paired amis O'lo ; distal breadth of the former 

 0-12, of the latter 0'06. 



Habitat. — North Atlantic, Station 354, surface. 



