1642 THE VOYAGE OF H.M.S. CHALLENGER. 



hexagonal meshes, the bars of which bear the same verticils, each composed of four thin quadri- 

 dentate anchor-threads. At each nodal point arises a slender, smooth, radial spine, which bears at 

 its distal end a verticil of four large, curved, terminal branches. 



Dimensions. Diameter of the inner shell 0'4, of the outer 3'2. 



Habitat. South Atlantic, Station 332, depth 2200 fathoms. 



Order III. PILEOGROMIA, Haeckel, 1879. 



Definition. PH^EODARIA with a simple, not bivalved lattice-shell, which assumes 

 very different forms, but is always provided with a peculiar mouth and peristome on the 

 oral pole of the main axis. Central capsule always excentric, placed in the aboral half 

 of the shell-cavity. 



Family LXXVIII. CHA LLENGERIDA, John Murray (PL 99). 



Challengerida, John Murray, 1876, Proc. Eoy. Soc. Lend., vol. xxiv. p. 471, pi. xxiv. figs. 1, 2. 



Definition. PH^EODARIA with a monaxonial, usually ovate or lenticular shell, 

 which exhibits a peculiar, fine, regularly hexagonal, diatomaceous structure, and is 

 usually provided with teeth on the mouth, but without articulated feet. Central capsule 

 excentric, placed in the aboral .half of the shell-cavity. 



The family Challengerida represent a large, peculiar, and interesting group of 

 PH^EODARIA, which are, for the most part, inhabitants of great depths, and were 

 perfectly unknown before the discoveries of the Challenger. The first note on these 

 remarkable Eadiolaria was given in 1876 by John Murray, in his Preliminary Reports 

 on Work done on board the Challenger (Proc. Roy. Soc. Lond., vol. xxiv. pp. 471, 

 536, pi. xxiv. figs. 1, 2). He described the peculiar exceedingly beautiful tracery of 

 their shell, similar to that of the Diatomacese, the enclosed central capsule coloured by 

 carmine, and the surrounding mass of black-brown pigment lumps (the phseodium). 

 " At times these Challengerida come up with a good deal of sarcode outside of the 

 shell, and two specimens have been seen to throw out elongated pseudopodia" (loc. cit., 

 p. 536). He found also the shells in the Radiolarian ooze of the deep sea. The 

 number of different forms found in the collection of the Challenger is so great, that I 

 can describe in the following pages not less than six genera and fifty-eight species. A 

 part of these have already been figured by Dr. John Murray in the Narrative of the 

 Challenger Expedition, vol. i. p. 226, PL A, 1885. 



In my first preliminary note on the PH^EODARIA, in 1879, I gave a stricter definition 



