224 



THE VOYAGE OF H.M.S. CHALLENGER. 



of numerous radial spines, which meet in the centre of the capsule. In most cases, 

 twenty such spines are present, and in accordance with a curious law, discovered by- 

 Johannes Miiller, these are geometrically divided into five zones, each containing four of 

 these spines (figs. 89, 90). In the Acanthometrse these give rise to no special perforated 

 shell, whilst in the Acanthophractse this is developed into many varied and delicate forms. 

 " The Spumellaria include that large group of Radiolaria whose simple capsular 

 membrane is perforated by minute pores, and whose nucleus divides only at a later 



Fig. 95. — Lithocoronis challengeri, n. gen. et sp. 



stage (at the time of reproduction) into numerous spore-nuclei. In only a few families 

 (Thalassicollida, Collozoida) the skeleton is entirely wanting, or is reduced to single 

 scattered spicules (Thalassosphserida, Sphserozoida). The skeleton usually consists of a 

 latticed sphere (Sphaeroida), which is developed into multifarious forms — stars, disks, 

 concentric, sponge-like, flinty shells, &c. (see figs. 91 and 92). These are often rendered 

 conspicuous by radial spines and processes of curious and varied form. 



" The Nassellaria are distinguished from the two preceding groups by the peculiar 

 structure of their central capsule, from which the pseudopodia protrude only at a per- 



