382 THE VOYAQE OF H.M.S. CHALLENGER. 



distal chamber a circle of large square meshes. The breadth of the pores is eight to twelve times 

 that of the bars between them. The whole surface is covered with small bristle-like spines. 



Dimensions. — Total length of the cortical shell 014, greatest breadth (in the equator of each 

 proximal chamber) 0-07 ; meshes 0-008 to 0-015, bars 0-002, spines 0-01. 



Habitat. — Pacific (Philippine and Californian Sea), 3300 and 2300 fathoms, Ehrenberg ; Station 

 200, depth 250 fathoms; Station 253, depth 3125 fathoms. 



15. Panartus 'pluteus, ii. sp. (PI. 40, fig. 2). 



Both proximal chambers kidney-shaped, with irregular, roundish pores, twice to four times as 

 broad as the bars ; their surface everywhere covered with short conical thorns. From both polar 

 circles arise ten to twelve radial rods, which bear a fenestrated cap, and form thus either the 

 beginning of a second, external, cortical shell, or (if remaining thus) two imperfect distal chambers. 

 The spherical segment, which forms theii- surface, is concentric with the proximal chambers, is per- 

 forated by the same irregular, roundish pores, and covered with numerous bristle-like spines. 



Dimensions. — Main axis of the cortical shell 0-17, equatorial axis (in the constriction) Q-OB ; 

 distance between the proximal and distal chambers 0-03 ; pores 0-003 to 001, bars 0-003 to 0-005. 



Habitat. — Pacific, central area. Station 272, depth 2600 fallionis. 



Genus 164. Peripanartus} n. gen. 



Definition. — P a u a r t i d a with double cortical shell and double medullary shell, 

 without polar spines or tubes on both poles of the main axis. 



The genus Peripanartuit differs from Panartus only in the develoj)ment of an 

 outer reticulated envelop, which mantle-like surrounds the shell and represents a second 

 or external cortical shell. This mantle or veil envelops either the whole internal 

 cortical shell or only both proximal chambers. Peripanartas exhibits the same rela- 

 tion to Panartus as in the foregoing ancestral family Cypassis bears to Cyphonium. 



Subgenus 1. Peripanartala, Haeckel. 

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



1. Peripanartus paUiatus, n. sp. 



Internal cortical shell with four kidney-shaped chambers of equal size and similar form, identical 

 with the cortical shell of Panartus tetrathalam.us and Panartus quadrijugus (PL. 40, fig. 3), with 

 irregular, roundish pores, twice to three times as broad as the bars. It differs from these two species 



1 Peripanartus = Panartics with muutle ; xtj/xaj'a^Toj. 



