EEPORT ON THE RADIOLARIA. 1681 



mouth of the shell, therefore placed in its main axis ; it is usually quite hidden in the 

 dark phseodium, which occupies the oral half of the shell-cavity, whilst the capsule lies 

 in the aboral half, The large nucleus of the central capsule and its double membrane 

 present the same characters as in the other PH^EODARIA. 



Synopsis of the Genera of Castanellida. 



,., . . /. ,,.,. . I Mouth smooth, . 705. Castanarium. 



No long radial main-spmes (in addition to the constant J 



short bristles of the sheU-suiface). | Mouth ^^ _ _ 7Q6 _ 



Long radial main-spines 

 scattered between the short 

 constant bristles of the " 

 shell-surface. 



Main spines simple. 



Mouth smooth, . . 707. Castanidium. 



Mouth dentate, . . 708. Castanissa. 



Mouth smooth, . . 709. Oastanopsis. 



Main spines branched. 



Mouth dentate, . .710. Castanura. 



Genus 705. Castanarium, 1 Haeckel, 1879, Sitzungsb. med.-nat. Gesellsch. 



Jena, Dec. 12, p. 5. 



Definition. C astanellida without radial main-spines, with a simple smooth 

 mouth. 



The genus Castanarium is the simplest form of all the Castanellida, and may be 

 regarded as the common ancestral form of this family. The simple spherical shell has a 

 smooth, toothless mouth and no larger radial spines; it is densely studded with the 

 simple, radial bristles, which are common to all Castanellida. The shell therefore is 

 very similar to those species of the Astrosphseride Acanthosphcera, which represent the 

 subgenus Rhapidococcus (compare above, p. 210, PL 26, fig. 3); it differs from the 

 latter in the possession of the shell-mouth, which is absent in all S p h ae r o i d e a. 



1. Castanarium darwini, n. sp. 



Pores regular, circular, hexagonally framed, three times as broad as the bars. Radial bristles 

 half as long as the radius. 



Dimensions. Diameter of the shell 0'3 to 0'4, of the pores 0'03. 



Habitat. South Atlantic (east of Patagonia), Station 318, depth 2040 fathoms. 



1 Castanarium = Shell similar to a chestnut, Costarica. 

 (ZOOL. CHALL. EXP. PART XL. 1886.) Rr 211 



