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



Dimensions. — Diameter of the spherical outer shell O'lo, inner shell Oil ; pores of the inner 

 0-01, bars 0-005. 



Hahitat. — Pacific, central area, Station 274, depth 2750 fathoms. 



Genus 299. Ciohotholus,^ n. gen. 



Definition. — T h o 1 o n i d a with simple cortical shell (without external veil), 

 composed of six hemispherical cupolas, ojjposite in pairs on the poles of three axes 

 perpendicular one to another, covering six sides of the cuboidal Larnacilla -shixped 

 central chamber (with medullary shell). 



The genus Cuhotholus differs from TJiolocuhus in the possession of a medullary 

 shell in the central chamber, and may be derived from this genus by its production ; 

 but it may also be derived from Staurotholus by apposition of two opposite domes on 

 the flat sides of the cross-shell. Sometimes all six domes are of the same size and 

 form, but commonly different in pairs. 



Subgenus 1. Cuhotholissa, Haeckel. 

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



1. Cuhotholus regularis, n. sp. (PI. 10, fig. 14). 



On the six sides of the cubical central chamber six hemispherical cupolas of the same size and 

 form. Surface smooth. Pores regular, circular, twice as broad as the bars ; eight in the basal 

 semicircle of each cupola. Medullary shell apparently spherical (?), connected with the eight 

 corners of the central chamber by eight radial beams, regularly disposed. (This species is 

 remarkable for the perfect symmetry of the shell, the six sides of which appear to be quite 

 .similar. It differs from the similar Tholocubus rctjularis in the possession of a medullary shell.) 



Dimensions. — Diameter of the cortical shell (equal in all three dimensive axes) 0"15 ; pores 

 O'Ol, bars 0'005 ; diameter of the medullary shell 0'04. 



Habitat. — Pacific, central area, Station 273, depth 2350 fathoms. 



2. Cuhothob'.s quadraticus, n. sp. 



Surface of the shell smooth. Both principal cupolas (on the poles of the longitudinal axis) 

 larger than the four other cupolas, which have the same size and lie cross-wise in the equatorial 

 plane. (Therefore two of the three fundamental axes equal, the third larger.) Pores subregular, 

 circular, three times as broad as the bars ; ten to twelve in the semicircle of each cupola-basis. 



Dimensions. — Major axis 0'16, minor axis 012; pores 0'012, bars 0'004. 



Habitat. — Indian Ocean, Zanzibar, PuUen ; depth 2200 fathoms. 



1 Cuhotholus = Bhe]l with cupolas disposed on six cube-sides ; *u/3of, 66M;. 



