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



inner cortical shell is protected by an outer larger cupola, and besides this the whole shell 

 is enveloped by a thin ellipsoidal veil (PI. 10, fig. 15). Therefore this species may be 

 the representative of a peculiar genus, the most highly developed of all Tholonida 

 Tholothauma. 



1. Cubotholonium sphceroides, n. sp. 



Outer cortical shell (or veil) spherical, with smooth surface ; network very delicate, with very 

 thin bars and very small irregular, roundish pores. Inner cortical shell simple, composed of 

 six hemispherical cupolas, surrounding the six sides of the cubical central chamber, which encloses 

 a spherical medullary shell (one-third as large as itself). Network of the inner cortical shell 

 regular, with circular pores of the same breadth as the bars ; twelve to fourteen in the basal semi- 

 circle of one cupola. 



Dimensions. Diameter of the spherical outer shell - 2, of the inner cortical shell 015 ; pores 

 and bars of the latter O'OOG. 



Habitat. Indian Ocean, Zanzibar, Pullen, depth 2200 fathoms. 



2. Cubotholonium ellipsoides, n. sp. (PL 10, fig. 15). 



Tholothauma ellipsoides, Haeckel, 1883, MS. 



Outer cortical shell (or veil) ellipsoidal, with very thin irregular network and thorny surface. 

 Inner cortical shell double, with six double, flatly vaulted cupolas, surrounding the six sides of the 

 Z,arnacilla-sh&ped. central chamber ; the double domes of each shell are in opposite pairs somewhat 

 larger than the alternating pairs. Pores subregular, circular, about the same breadth as the bars ; 

 eight to twelve in the basal semicircle of one cupola. Central chamber with ellipsoidal medullary 

 shell. Eadial spines short, very numerous. 



Dimensions. Major axis of the outer cortical shell 0'28, minor 0'24 ; major axis of the inner 

 cortical shell 016, minor axis 014 ; pores and bars O'OOG ; medullary shell 0'03. 



Habitat. Pacific, central area, Station 271, depth 2425 fathoms. 



Family XXVIII. ZON AKID A, n. fam. (PL 50, figs. 9-12). 



Definition. Larcoidea with regular, completely latticed cortical shell, distin- 

 guished by two to four or more annular constrictions, which lie (all or partly) in the 

 dimensive planes (sagittal, transverse, or lateral), and by which four to eight or more 

 vaulted cupolas or dome-like chambers become separated. In the centre of this 

 chambered cortical shell lies constantly a trizonal or Larnacilla-shaped medullary shell. 



The family Zonarida comprises a small number of peculiar Larcoidea, resem- 

 bling the Tholonida in the composition of the polythalamous cortical shell by a number 

 of cupolas or dome-shaped protuberances. But the disposition and origin of these latter 



