REPORT ON THE RADIOLARIA. 377 



The genus Panartus represents the common ancestral form of all Panartida, 

 as all other genera of this subfamily must be derived from it, and are only further 

 developmental stages, from an ontogenetic as well as from a phylogenetic point of view. 

 The cortical shell of Panartus is constantly composed of four fenestrated chambers 

 jointed to one another in the main axis; both proximal chambers are separated from one 

 another by the equatorial ring-like constriction, in the centre of which lies the double 

 medullary shell ; both distal chambers are separated from the former by two other 

 annular constrictions (in planes parallel to the equatorial plane). All four chambers 

 may exhibit the same (kidney-shaped) form and structure (in the subgenera Panartella 

 and Panartoma) ; or the proximal chamber may differ more or less in shape and size 

 from the distal (in the subgeuera Panartissa and Panartura). The outer surface of 

 the cortical shell is sometimes smooth (as in Panartella and Panartissa), at other times 

 spiny or thorny (as in Panartoma and Panartura). The double medullary shell is 

 sometimes spherical, or commonly compressed at both poles and spheroidal or lenticular. 



Subgenus 1. Panartella, Haeckel. 



Definition. Surface of the cortical shell smooth, without spines or thorns. All 

 its four chambers exhibit nearly the same form and structure. 



1. Panartus tetraplus, n. sp. 



All four chambers of the cortical shell of the same form, size, and structure, kidney-shaped, twice 

 as broad as long. Pores rather regular, hexagonal, all nearly of the same size and form, four times as 

 broad as the thin bars ; five to six pores on the half meridian, nine to ten on the half equator of 

 each chamber. Surface of the cortical shell smooth, its main axis three times as long as its 

 equatorial axis (in the median constriction). Both concentric medullary shells spherical; the equatorial 

 axis of the outer half as long as that of the cortical shell. (All four chambers of this species have 

 the same appearance as the two proximal chambers of Panartus diploconus, PL 40, fig. 1.) 



Dimensions. Main axis of the cortical shell O21, equatorial axis 0'07 ; breadth of every 

 chamber O09 ; meshes O013, bars O03. 



Habitat. Central area of the Pacific, Stations 270 to 274, depth 2350 to 2925 fathoms. 



2. Panartus tetracolus, u. sp. 



All four chambers of the cortical shell of the same form, size, and structure, kidney-shaped, 

 twice as broad as long. Pores regular, circular, with hexagonal frame, twice as broad as the bars ; 

 six to seven pores on the half meridian, ten to twelve on the half equator of each chamber. Surface 

 of the cortical shell smooth ; its main axis three times as long as the equatorial axis. Both 

 concentric medullary shells spheroidal, somewhat compressed at both poles ; the equatorial axis 



(ZOOL. CHALL. EXP. PART XL. 1885.) Er 48 



