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



Genus 10. Thalassoplancta? Haeckel, 1862, Monogr. d. Radiol., p. 261. 



Definition. T halassosphserida with numerous large alveoles in the calymma 

 (but not in the central capsule), and with numerous simple, needle-shaped spicula around 

 the central capsule. 



The genus Thalassoplancta was founded by me in 1862 for a Radiolarian with 

 simple hollow needles in the calymma, which was afterwards recognised as a Phseodarium, 

 belonging to Cannorhaphis. We here retain this name for a true Thalassosphserid, very 

 similar to the latter, but distinguished by the absence of the phseodium and the solid 

 not hollow needle-shaped spicula, which are scattered in the alveolated calymma. 

 Thalassoplancta can be regarded as the solitary form of the social Belonozoum? 



1. Thalassoplancta longispicula, n. sp. 



Spicula long and thin, cylindrical, smooth, more or less bent, pointed at both ends, similar to 

 those of Thalassoplancta cavispicula. Central capsule thin-walled, without oil-globules, four times as 

 broad as the nucleus, which encloses one single nucleolus. 



Dimensions. Diameter of the capsule 0'6, of the nucleus 0'15, of the calymma 4 mm. 



Habitat. North Atlantic, Fseroe Channel (Gulf Stream), John Murray. 



2. Thalassoplancta brevispicula, n. sp. (PI. 2, fig. 2). 



Lampoxanthium brevispiculum, Haeckel, 1882, Atlas. 



Spicula short and thick, thorny, irregularly curved, pointed at both ends, very numerous. In 

 the observed specimen all spicula were aggregated in the outer part of the voluminous calymma, 

 whilst the inner alveolated part was devoid of them. Central capsule thick walled, with a layer of 

 large oil-globules on its inner surface, twice as broad as the large nucleus which contains numerous 

 nucleoli. 



Dimensions. Diameter of the central capsule P 5, of the nucleus 0'2, of the calymma 2'5. 



Habitat. South Atlantic, Station 334, surface. 



Genus 11. Lampoxanthium^ n. gen. 



Definition. T halassosphserida with numerous large alveoles in the calymma 

 (but not in the central capsule), and with numerous branched or compound spicula in 

 the calymma. 



1 Thalassoplancta Floating on the sea ; 



2 Compare Thalassoplancta cavispicula, Monogr. d. Radiol., 1862, p. 261, Taf. iii. figs. 10-13. 



3 Lampoxanthium, = Scum-burdock ; 



