1524 THE VOYAGE OF H.M.S. CHALLENGER. 



The total number of PH^EODARIA, hitherto described and illustrated by figures, 

 amounts therefore to seventeen species, viz., the seven species first described by myself (in 

 1862) ; the six new species figured by Dr. John Murray (in 1876) ; the three new species 

 discovered by Hertwig (in 1879) and the single species last-mentioned described by 

 Biitschli (in 1882). The rich collection of the Challenger has added to this small number 

 such an astonishing wealth of new and remarkable forms, that I can describe in the 

 following system of PHJEODARIA not less than eighty-four genera and four hundred and 

 sixty-five species. These belong to fifteen different families and four different orders. 

 But this great number is probably only a small part of the numerous interesting 

 PH^EODARIA, which are abundantly distributed over all the oceans ; those (e.g.) of the 

 Indian and of the Arctic Oceans are almost unknown. 



The great majority of these wonderful PH^EODARIA are inhabitants of the deep-sea, 

 mainly of the southern hemisphere, and are so common in many stations explored by the 

 Challenger, that its collection contains many thousands (or rather hundreds of thousands) 

 of well-preserved specimens. A smaller part of the legion is found on the surface, widely 

 distributed over all oceans; some of these are very common (as, e.g., Aulacantha, 

 Aidosphcera, Sagosphcera, Ccelodendrum, Castanella, &c.) and it is difficult to explain 

 how they could entirely escape the eyes of all former observers. 



The three general characters which distinguish the PH^EODAEIA easily and constantly 

 from all the other Radiolaria are the following: (l) the double membrane, a thick 

 outer and a thin inner envelope, of the big central capsule ; (2) its typical main- 

 opening or astropyle, placed on the oral pole of the main axis, and distinguished 

 by a peculiar radiate operculum, with tubular proboscis ; (3) the phseodium, or the 

 peculiar voluminous pigment-body, which constantly lies in the oral half of the calymma, 

 surrounds the oral part of the central capsule, and is composed of numerous phseodella, 

 or singular pigment-granules of green, olive, brown or black colour. 



Besides these three general and never failing marks of the PH^EODARIA, the majority 

 of this legion (but by no means all) possess the three following peculiarities; (1) two 

 parapylse or accessory openings of the central capsule, placed laterally (at the right and 

 left) on the aboral pole of the main axis (wanting in the Challengerida, Medusettida, 

 Castanellida, and perhaps in some other families) ; (2) a characteristic skeleton which is 

 always extracapsular, wanting only in the Phaeodinida, incomplete in the Cannorrhaphida 

 and Aulacanthida, but perfectly developed and of very various shapes in the twelve other 

 families ; usually this silicated skeleton is composed of hollow tubules, which are filled up 

 by jelly (PANSOLENIA) ; but in some families it is composed of ordinary solid network, 

 not different from that of the other Radiolaria, eg., especially in the Castanellida and 

 Sagosphserida ; (3) an extraordinary size of the body, as well of the central capsule 

 and its nucleus, as of the extracapsular skeleton ; the majority of PH^EODARIA have a 

 diameter of 1 to 2 mm., and are therefore from ten to twenty times as large as the 



