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



Subfamily 2. STAUROTHOLIDA, Haeckel. 



Definition. T holonida with diaxial growth ; cupolas crossed in pairs, opposite 

 on the poles of two axes, perpendicular one to another. (Shell commonly five- 

 charnbered, with four domes, cross-wise surrounding the central chamber.) 



Genus 293. Tholostaurus, 1 n. gen. 



Definition. T holonida with simple cortical shell (without external veil), 

 composed of four hemispherical cupolas in cross-form, opposite in pairs on the poles of 

 two axes perpendicular one to another ; central chamber simple (without medullary 

 shell). 



The genus Tholostaurus is the most simple form of the Staurotholida, or the 

 Tholonida with four crossed hemispherical cupolas, lying on the poles of two axes 

 perpendicular one to another. The central chamber communicates by four wide open- 

 ings with the four domes, and contains no medullary shell. Tholostaurus may 

 originate either from Tholartus by apposition of two opposite cupolas between the first 

 pair, or from Staurotholus by loss of the medullary shell. 



Subgenus 1. Tholostaurantha, Haeckel. 

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



1. Tholostaurus quadrigatus, n. sp. 



All four cupolas nearly of the same size and form, subregular. Surface smooth, without radial 

 spines. Pores subregular, circular, four times as broad as the bars ; eight to ten pores in the basal 

 semicircle of one cupola. 



Dimensions. Diameter of the shell 012 ; pores O'OOS, bars 0002. 



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



2. Tholostaurus cruciformis, n. sp. 



Two opposite cupolas larger than the two others. Surface rough, without radial spines. Pores 

 regular, circular, hexagonally framed, twice as broad as the bars ; twelve to fourteen in the basal 

 semicircle of one cupola. 



Dimensions. Major axis of the shell 016, minor axis 012 ; pores O'OOG, bars 0'003. 



Habitat. Pacific; central area, Station 265, depth 2900 fathoms. 

 1 Tholostaurus -Cross of four cupolas ; 60*0;, 



