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



Subgenus 2. TJwlocubitus, Haeckel. 

 De/in it ion. Snvf ace of the shell with radial spines or thorns. 



3. Tholocubus tesseralis, n. sp. (PI. 10, fig. 16). 



Surface of the shell with numerous (eight to sixteen) thin and long, bristle-shaped radial 

 spines (the greater part broken off in the figured specimen) ; pores subregular, circular, three to four 

 times as broad as the bars ; ten to twelve in the semicircle of one cupola. 



Dimensions. — Major axis of the shell 016, minor axis 0"14 ; pores O'Ol, bars 0'0027. 



Sahitat. — Pacific, central area. Station 271, depth 2425 fathoms. 



Genus 298. Tholonium,^ n. gen. 



Definition. — Tholonida with double cortical shell (with external veil), composed 

 of six hemispherical cupolas, opposite in pairs on the poles of three axes perpendicular 

 one to another, covering six sides of the simple cuboidal central chamber (without 

 medullary shell). 



The genus Tliolonium (PI. 10, fig. 17) difl'ers from the preceding TJiolocuhus only 

 in the duplication of the cortical shell. The outer (secondary) shell forms either a 

 simple (spheroidal or ellipsoidal) thin veil around the inner (primary) shell, or both 

 shells are of the same form, with six corresponding cupolas. Possibly Tliolonium is 

 the ofi'spring of Cubotliolonium, ha^dng originated l^y loss of the medullary shell. 



Subgenus 1. Tliolonetta, Haeckel. 

 Definition. — Surface of the shell smooth or rough, without radial spines or thorns. 



1. Tliolonium bicubicum, n. sp. 



Outer shell with six hemispherical dome-shaped protuberances, corresponding to those of the inner 

 shell. Both shells connected by numerous radial beams. Surface of the outer shell smooth ; its 

 network nearly of the same shape as that of the inner, with subregular, circular pores, twice as 

 broad as the bars ; ten to fifteen pores on the semicircle of one cupola. 



Dimensions. — Diameter of the outer shell 0'14, of the inner 012 ; pores of the latter 0'006, bars 

 0-003. 



Hahitat. — South Atlantic, Station 325, depth 2650 fathoms. 



1 T/ioZoJiMim = Shell witli cupolas ; h'hu'jinu. 



