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



8. Thalassoxanthium ovodimare, n. sp. 



Spicula all geminate, composed of a simple, very short axial rod and three diverging shanks 

 or branches on each end of it ; the shanks are very thin, straight, or little curved, and eight to ten 

 times as long as the axial rod. The spicula are quite smooth, as in the similar Sphcerozoum ovodimare 

 (in which, however, the axial rod is much longer). Central capsule transparent, without oil-globules, 

 twice as broad as the nucleus. 



Dimensions. Diameter of the capsule 04, of the nucleus - 2, length of the spicula 01 to 0'2. 



Habitat. Central Pacific, Station 273, surface. 



9. TJialassoxanthium punctatum, n. sp. 



Spicula all geminate-triradiate, composed of a simple middle rod and of three diverging shanks 

 on each end of it ; the shanks are thorny with small spinules and shorter than the axial rod, very 

 similar to the common Sphcerozoum punctatum. Central capsule dark, with numerous (twenty to 

 thirty) oil-globules on the inside of the membrane, three times as broad as the nucleus. 



Dimensions. Diameter of the capsule 0'3, of the nucleus 01, length of the spicula 

 0-05 to 0-2. 



Habitat. Central Pacific, Station 274, surface. 



10. Thalassoxanthium octoceras, n. sp. (PL 2, fig. 6). 



Spicula all geminate-quadriradiate, composed of a simple short middle rod and of four diverging 

 shanks on each end of it ; the shanks are quite smooth, irregularly curved or bent, and four to 

 eight times as long as the middle rod. Central capsule dark, filled with pigment-granules, without 

 oil-globules, four times as large as the nucleus. 



Dimensions. Diameter of the capsule 0'5, of the nucleus 012, length of the spicula 0'2 to 0'4. 



Habitat. Indian Ocean, Madagascar, Rabbe. 



Genus 9. Physematium, 1 Meyen, 1834, Nova Acta Acad. Nat. Curios., 

 vol. xvi., Suppl., p. 286 (p. 162). 



Definition. T halassosphserida with large numerous alveoles within the 

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

 in the calymma. 



The genus Physematium is, together with the colony-forming Sphcerozoum, the 

 first Radiolarian which was observed in the living state, described in 1834 by Meyen. It 

 is most nearly allied to Tlialassolampe, and has the same large roundish alveoles within 

 the central capsule, which reaches therefore an extraordinary size, 5 to 10 mm. It 



1 Physematium = Small vesicle ; 



