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



3. Ti'izonium hexagonium, n. sp. 



Central chamber spherical. Lateral girdle hexagonal, with parallel sides, twice as lone as 

 broad. Four gates triangular, twice as broad as high. Eleven to twelve pores on the half equator, 

 sixteen to eighteen on the half meridian. No radial spines. 



Dimensions. — ^Diameter of the central chamber 0'025 ; length of the lateral gu'dle 0"08, breadth 

 0-04 ; height of the gates 0-018, breadth 0-036. 



Habitat. — Pacific, central area, Station 266, depth 2750 fathoms. 



4. Trizonium octogonium, n. sp. 



Central chamber spherical. Lateral girdle octagonal ; two lateral sides of the octagon twice as 

 long as the two polar sides and the four diagonal sides. Four gates hexagonal, one and a half 

 times as broad as high. Nine to ten pores on the half equator, twelve to fourteen on the half 

 meridian. No radial spines. 



Dimensions. — Diameter of the central chamber 0-02 ; length of the lateral girdle O'Ol, breadth 

 0-07 ; height of the gates 0-04, breadth 0-06. 



Habitat. — Indian Ocean, surface ; Ceylon, Haeckel. 



Subgenus 2. Trizonitis, Haeckel. 

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



5. Trizonium pleurobelonium, n. sp. 



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

 Four gates nearly circular. Ten to eleven pores on the half equator, fifteen to sixteen on the half 

 meridian. Two opposite conical spines on the poles of the lateral axis. 



Dimensions. — Diameter of the central chamber 0-02; length of the lateral girdle O'OS, breadth 

 0-06 ; height and breadth of the gates 0-025. 



Habitat. — South Atlantic, oft' Buenos Ayres, Station 323, depth 1900 fathoms. 



6. Trizonium amphibelonitim, n. sp. 



% Echinosphmra datura, E. Hertwig (jxirtim), 1879, Organismus d. EaJiol., p. 54, Taf. iv. figs. 8, 8a. 



Central chamber lentelliptical. Lateral girdle lanceolate, nearly one and a half times as long as 

 broad. Four gates subtriangular. Eight to nine pores on the half equator, ten to twelve on the 

 half meridian. Two opposite thin and long spines on the poles of the principal axis, numerous 

 shorter radial spines on the whole surface. Possibly this species is identical with one of the three 

 different Larcoidea which R Hertwig has described as Echinosphccra datura. His fig. 8, Taf. iv., 

 would be the aspect fi-om the sagittal gircUe. 



