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



Subgenus 2. Dizonitis, Haeckel. 

 Definition. Shell with radial spines or thorns, symmetrically disposed. 



4. Dizonium pleuracanthum, n. sp. (PI. 9, fig. 2). 



Central chamber of the shell nearly spherical, smooth. Lateral girdle elliptical, one and a third 

 times as long as broad, three times as long as the central chamber. Four gates transverse-elliptical, 

 one and a half times as broad as high. Two conical spines, opposite on the poles of the lateral axis. 



Dimensions. Diameter of the central chamber 0'03 ; length of the lateral girdle 01, breadth 

 0-075 ; height of the gates 0'026, breadth 0'04. 



Habitat. Western Tropical Pacific, Station 224, depth 1850 fathoms. 



5. Dizonium amphacanthum, n. sp. 



Central chamber elliptical. Lateral girdle elliptical, twice as long as broad. Four gates heart- 

 shaped, about as high as broad. Two conical spines, opposite on the poles of the principal axis. 



Dimensions. Length of the central chamber 0'03, breadth 0'02; length of the lateral girdle O'l, 

 breadth 0'05 ; height and breadth of the gates 0'03. 



Habitat. Pacific, central area, Station 270, depth 2925 fathoms. 



6. Dizonium stauracanthum, n. sp. (PL 9, fig. 3). 



Central chamber spherical. Lateral girdle elliptical, one and a third times as long as broad. 

 Four gates elliptical, one and a half times as broad as high, halved by an axial beam (as in Odopyle). 

 Four conical radial spines opposite in pairs, two on the poles of the principal, two on the poles 

 of the transverse axis. 



Dimensions. Diameter of the central chamber 0'025 ; length of the lateral girdle 0'09, breadth 

 0-06 ; height of the gates 0'024, breadth 0'036. 



Habitat. South Atlantic, Station 332, depth 2200 fathoms. 



7. Dizonium octacanthum, n. sp. 



Central chamber spherical. Lateral girdle elliptical, one and a half times as long as broad. 

 Four gates kidney-shaped, twice as broad as high. Eight radial spines, opposite in pairs in two 

 crossed diagonal planes. 



Dimensions. Diameter of the central chamber 0'02 ; length of the lateral girdle 0'07o, breadth 

 0-05 ; height of the gates 0'02, breadth 0'04. 



Habitat. Pacific, central area, Station 272, surface. 



