REPORT ON THE RADIOLARIA. 637 



Genus 281. Trizonium, 1 n. gen. 



Definition. P y 1 o n i d a with simple, spherical or subspherical, central chamber, 

 surrounded by three latticed girdles, one smaller (primary) transverse, one larger 

 (secondary) lateral, and one (tertiary) sagittal girdle. 



The genus Trizonium represents the most highly developed form of the Haplozonaria, 

 with three complete elliptical latticed girdles, crossed at right angles and lying in 

 the perimeter of the three dimensive planes. Commonly the first (transverse) girdle is 

 the smallest, immediately connected with the spherical or lentelliptical central chamber. 

 The minor axis of the second (lateral) girdle is identical with the major axis of the first 

 girdle. The third (sagittal) girdle is either larger than both others, or intermediate 

 between them. If the four gates between the girdles become afterwards closed by 

 lattice-work, the " trizonal shell " of Trizonium passes over into the typical Larnacilla, 

 the ancestral form of a great many Larcoidea. 



Subgenus 1. Trizonaris, Haeckel. 

 Definition. Shell smooth or rough, without radial spines or thorns. 



1. Trizonium tricinctum, n. sp. (PL 9, fig. 4). 



Central chamber of the shell elliptical. Lateral girdle elliptical, one and a half times as long 

 as broad. Four gates kidney-shaped, one and a half times as broad as high. Ten to eleven pores 

 on the half equator, fourteen to sixteen on the half meridian of the lentelliptical shell. No radial 

 spines on the surface. 



Dimensions. Length of the central chamber 0'024, breadth 0'016 ; length of the lateral girdle 

 0-075, breadth 0'05; height of the four gates 0'026, breadth 0'04. 



Habitat. Pacific, central area, Station 272, depth 2600 fathoms. 



2. Trizonium constrictum, n. sp. 



Central chamber elliptical. Lateral girdle violin-shaped, on both sides in the middle constricted, 

 twice as long as broad. Four gates transverse-elliptical, twice as broad as high. Eight to nine 

 pores on the half equator, twelve to thirteen on the half meridian. No radial spines. 



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

 0-09, breadth (in the middle) 0'045 ; height of the gates 0'022, breadth 0'044. 



Hulitat. Pacific, central area, Station 263, surface. 



1 Trizonium = With three girdles ; T 



