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



1. Triolena primordialis, n. sp. (PI. 48, fig. 12). 



Arm-chambers trapezoid, nearly square, of tlie same size as the circular, lenticular, primordial, 

 central chamber. Surface of the disk smooth. 



Dimensions.— DiaxaQier of the shell 0"045, of the central chamber 0'015, of each arm 0'015. 

 Habitat. — Central Pacific, Station 272, depth 2600 fathoms. 



2. Triolena tribelone, u. .sp. 



Arm-chambers lanceolate, of the same breadth as and twice the length of the triangular, central 

 chamber ; at the pointed end of each arm is a conical terminal spine (in the equatorial plane). 

 Surface of the disk thorny. 



Dimensions. — Diameter of the shell 0'05, of the central chamber 0"015 ; length of the arms 

 0-02, breadth 0-016. 



Habitat. — North Pacific, Station 244, depth 2900 fathoms. 



3. Triolena trispinosa, n. sp. 



Arm-chambers ovate, in the basal half nearly as broad as the hexagonal central chamber, at the 

 pointed distal end with a strong conical radial spine of double the length. Surface rough. 

 Dimensions. — Diameter of the shell 0"55, of the central chamber 0'02. 

 Habitat. — Western Tropical Pacific, Station 225, depth 4475 fathoms. 



4. Triolena hexahelone, n. .sp. 



Arm-chambers nearly triangular, at the base half as broad as the hexagonal central chamber, 

 at the truncate distal end one and a half times as broad, and armed with two radial conical spines 

 (in the equatorial plane). Surface of the disk smooth. 



Dimensioiis. — Diameter of the shell 0"06, of the central chamber 0'02. 



Habitat. — South Pacific, Station 295, depth 1500 fathoms. 



5. Triolena trigonalis, n. sp. 



Arm-chambers nearly triangular, at the base half as broad as the circular central chamber, at 

 the concave lunulate distal end twice as broad, and armed with four conical radial spines (two on 

 each side of the equatorial plane). Surface thorny. 



Dimensions. — Diameter of the shell 0'05, of the central chamber O'OIS. 



Habitat. — Central Pacific, Station 271, depth 2425 fathoms. 



