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



circular pores, three to four times as broad as the bars. All following chambers cap-like, tapering 

 towards both poles, with more irregular, roundish pores, with a circle of ten to twelve larger square 

 pores at the base. Middle cortical shell with smaller roundish pores. Outer cortical .shell with 

 larger polygonal, quite irregular pores. Both medullary sheUs lenticular. Polar tubes conical or 

 cylindrical with conical apex, of very variable length, sometimes not longer than one internal 

 chamber, at other times twice to four times as long (in the figured specimen not fully developed, as 

 also a part of the shells). Differs from Zyrjocamfc chrysalis only by the production of polar tubes. 



Dimensions. — Length of the six-chambered inner cortical shell 0-25, of the middle 0"3, of the 

 outer 0'35; greatest breadth of the first 0'07, of the second O'll, of the third 0'14; other measures 

 the same as in Zygocampe chrysalis; length of the tubes 0-05 to 012 or more. 



Habitat. — Pacific, central area. Stations 270 to 274, depth 2350 to 2925 fathoms. 



Suborder V. DISCOIDEA, Haeckel (Pis. 31-38, 41-48). 



Discida vel Discoidea, Haeckel, 1862, Monogr. d. Radiol., pp. 56, 476. 

 Discoida, Discoidea, Discida, Haeckel, 1878, Protistenreich, p. 103. 



Definition. — Spumellaria with discoidal or lenticular central capsule (often -n-itli 

 radial prolongations, rarely allomorpliic) ; with discoidal or lenticular fenestrated 

 siliceous shell (often with radial spines or fenestrated arms, rarely allomorphic). Growth 

 reduced or diminished in the direction of one dimensive axis. 



The section Discoidea comprises those Spumellaria in which the fenestrated 

 shell is more or less discoidal or lenticular, flattened or compressed in the direction of 

 one axis. The geometric fundamental form of the latticed shell, which in the 

 S p h se r o i d e a is a sphere, here becomes a flat disk, like a medal, or a biconvex lens, 

 sometimes also a biconcave lens. The Discoidea can be derived from the S p h a3- 

 r o i d e a by shortening of one axis. This shortened vertical axis is the main axis of the 

 disk ; both its poles are constantly equal. Perpendicular to this axis is the equatorial 

 plane of the disk by which it becomes divided into equal halves. In the simplest forms 

 of Discoidea all axes of this horizontal equatorial plane (all " equatorial axes " or 

 " cross axes ") are equal ; in the most of the genera and species these cross axes are 

 different, so that rays of stronger growth ("perradii") alternate with rays of weaker 

 growth ("interradii"). The number of these cross axes distinguishable is commonly 

 two to four, rarely more. In the direction of these are developed either radial marginal 

 spines or spongy arms. 



The order Discoidea was founded in my Monograph (1862, p. 476) as the family 

 "Discida" (Radiolaria with flat discoidal or biconvex lenticular shell), comprising the 



