18 THE VOYAGE OF H.M.S CHALLENGER. 



three-fourths that of the whole jelly-sphere. Nucleus profusely branched or papillated, its 

 spherical surface covered with numerous (more than a hundred) finger-shaped obtuse blind sacs, 

 about as long as its radius. Protoplasm of the central capsule forming a loose network between 

 the large roundish alveoles, in the cortical zone radially striped and containing one layer of large 

 dark oil-globules. These are regularly distributed on the inside of the capsule-membrane and 

 separated by intervals, twice as broad as its diameter, giving to the capsule-surface a spotted 

 appearance. Extracapsular jelly-envelope thin, yellowish, with very numerous and small xanthellae. 



Dimensions. Diameter of the whole jelly-sphere 5 mm., of the central capsule 4 mm., of the 

 nucleus 1'3 mm. 



Habitat. Antarctic Ocean, Station 154 (south of Kerguelen), surface. 



Genus 4. Thalassicolla, 1 Huxley, 1851, Ann. and Mag. Nat. Hist., ser. 2, vol. viii. p. 433. 



Definition. Thalassicollida without intracapsular alveoles, but with large roundish or 

 globular alveoles within the extracapsular calymma. Nucleus in the centre of the capsule 

 simple spherical, not branched. 



The genus Thalassicolla was proposed by Huxley in 1851, for a certain number of 

 different voluminous jelly-like Radiolaria, which he had observed living during his voyage 

 in the " Rattlesnake " through the tropical seas, and of which he gives an excellent descrip- 

 tion the first accurate observations on living Radiolaria. Johannes Miiller afterwards 

 removed from this genus the social genera Sphcerozoum and Collosphcera (formerly 

 Thalassicolla punctata), and retained as type of the genus Thalassicolla nucleata. In 1 862 

 in my Monograph I added two other species, Thalassicolla pelagica and Thalassicolla 

 zanclea, and later (1870) Thalassicolla sanguinolenta. Now I think it better to separate 

 the last two species as a new genus, Thalassophysa, characterised by the papillate or 

 branched nucleus, and to retain in Thalassicolla only those forms with simple spherical 

 nucleus. For both genera the extracapsular, voluminous, spherical calymma or jelly- 

 envelope, with numerous large alveoles, is characteristic. The membrane of the central 

 capsule in Thalassicolla is now structureless (subgenus Tfialassicollarium, with three 

 species), now characterised by a peculiar structure, prominent ridges on the inside of the 

 membrane, which form a network with polygonal plates, resembling an epithelium 

 (PI. 1, fig. 5& ; subgenus Thalassicollidium, with four species). Of the seven species 

 here described, two are cosmopolitan, widely distributed, and common ; one is Medi- 

 terranean, one Atlantic, and three Pacific. 



Subgenus 1. Thalassicollarium, Haeckel. 



Definition. Membrane of the central capsule structureless, only perforated by 

 innumerable very small radial pores. 



1 Thalassicolla = Sea-jelly, 



