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



of the outer almost equals half that of the cortical shell. (All four chambers of this species 

 exhibit the structure of the two proximal chambers of Peripanartus amphiconus, PL 40, fig. 5.) 



Dimensions. Main axis of the cortical shell 0'24, equatorial axis O08; breadth of every chamber 

 O'Ol ; meshes O'Ol, bars 0'005. 



Habitat. Equatorial Atlantic, Station 348, depth 2450 fathoms. 



3. Panartus tetrameres, 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, circular, without hexagonal frame, about as broad as 

 the bars ; five to six 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, compressed ; the outer half as broad as the constriction. 

 (This species is very much like Ommatoeampe increscens, Stohr, 1880, loc. cit., Taf. ii. fig. 2, and may 

 be considered as the ancestral form of it.) 



Dimensions. Main axis of the cortical shell 0'2, equatorial axis 0'065 ; breadth of every 

 chamber 0'08 ; meshes and bars 0'005. 



Habitat. Fossil in the Tertiary rocks of Sicily, Caltanisetta, Haeckel. 



4. Panartus tetraphalangus, n. sp. 



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

 twice as broad as long. Pores irregular, polygonal (mostly pentagonal or hexagonal), four to eight 

 tunes as broad as the thin bars ; four to seven on the half meridian, eight to fifteen on the half 

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

 its equatorial axis. Both concentric medullary shells compressed, the outer, half as broad as the 

 constriction. 



Dimensions. Main axis of the cortical shell 0'26, equatorial axis 0'09 : breadth of every 

 chamber 012 ; meshes O'OOS to 0'02, bars O'OOl to 0'003. 



Habitat. Fossil in the rocks of Barbados, Haeckel. 



5. Panartus tetrathalamus, n. sp. (PL 40, tig. 3). 



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

 twice as broad as long. Pores irregular, roundish, twice to three times as broad as the bars ; a 

 circle of larger pores at the base of both distal chambers ; five to six pores on the half meridian, 

 ten to twelve on the half equator of each chamber. Surface of the cortical shell smooth ; its main 

 axis two and a half times as long as the equatorial axis. Both medullary shells spheroidal, com- 

 pressed, the outer one-third as broad as the constriction. (In the specimen figured spines begin to 

 arise from both distal chambers ; this forms a transition to Panartus quadrijugus.) 



Dimensions. Main axis of the cortical shell 0'18, equatorial axis O'O 1 ? ; breadth of every 

 chamber 0'09 ; meshes 0'003 to O'Ol, bars 0'002 to 0'004. 



Habitat. Cosmopolitan ; Mediterranean, Atlantic, Pacific, in various depths. 



