NARRATIVE OF THE CRUISE. 



223 



forated spot at one end of the longitudinal axis. The nucleus divides only at a late 

 stage into numerous small spore-nuclei. The variously shaped skeletons consist mostly 

 of a bell-shaped or conical perforated case, as in the Cyrtellaria (figs. 93, 94, 9G). 

 More rarely it consists only of a ring, or of a triradiate frame or a loose network of 

 siliceous rods, as in the Plectellaria (see fig. 95). The principal division of this order 

 is constituted by the family Cyrtida, in which the perforated shell is elongated 

 in the direction of the principal axis, and is separated by one, two, or more con- 

 strictions into two, three, or more segments (see figs. 93, 94, 96). 



" The Phseodaria have, like the fore- 

 going group, only one primary opening 

 for the protrusion of the pseudopodia, 

 but there are usually, in addition, two 

 (rarely, however, more) accessory open- 

 ings. Around the primary opening, and 

 outside the capsule, there is always a 

 large mass of blackish or greenish-brown 

 pigment, the ' Phseodium.' By means of 

 this and of the double membrane of the 

 central capsule, these are distinguished 

 from all other Radiolaria. They are also, 

 for the most part, much larger, and their 

 flinty skeleton usually consists of hollow 

 tubes. Up to the year 1872 only three 

 genera of Phaeodaria were known, namely, 

 those described in 1862 by Professor 

 Haeckel, under the designations Aula- 

 cantha, Aulosphcera, and Ccelodendrum. 

 During the Challenger Expedition, how- 

 ever, a great number of new genera and 

 species were discovered, many with very curious siliceous skeletons, these being, for the 

 most part, inhabitants of the deep sea. The most remarkable of these are, perhaps, the 

 Challengerida, several forms of which were briefly described and figured by Mr. Murray 

 in 1876 j 1 a number of species of two genera (Challengeria and Tuscarora) are shown 

 in PI. A. The unicellular, egg-shaped case has a peculiar structure, resembling that of 

 the Diatomacese (PI. A. figs. 1-7), and is, in most cases, armed about the mouth with 

 spines and hollow tubes (PI. A. figs. 1-12). 



" The majority of the Radiolaria are found near the surface of the open ocean, where 

 they frequently appear crowded together in large numbers. Many species are, however, 



Fig. 96. — Clathrocanium reg-inoe, n. sp. 



1 Proc. Boy. Soc, vol. xxiv. p. 535, 1876. 

 (narr. CHALL. EXP. — VOL. I. — 1884.) 



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