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



Dimensions. Major axis of the capsule 0'2, minor - 05 ; breadth of the nucleus 0'05, height 

 0'015 ; breadth of the calymma 0'6. 



Habitat. Tropical Atlantic, Station 347, surface. 



Subgenus 4. Actilarcus, Haeckel. 

 Definition. Central capsule lentelliptical, with three different axes. 



10. Actissa larcoides, n. sp. 



Central capsule lentelliptical ; with three different axes, bearing the proportion 4:3:2. Nucleus 

 spherical ; its diameter equal to the shortest radius of the capsule. No nucleoli visible. Protoplasm 

 transparent, with small vacuoles ; on the inside of the thin capsule-membrane numerous (fifty to 

 sixty) small oil-globules, regularly disposed. Calymma lentelliptical, twice as large as the central 

 capsule. 



Dimensions. Major axis or length of the capsule 0'2, middle axis or breadth 0'15, minor axis 

 or height 01 ; diameter of the nucleus 0'05, of the calymma - 3-0'4. 



Habitat. Central Pacific, Station 266, surface. 



Genus 2. Thalassolampe, 1 Haeckel, 1862, Monogr. d. Radiol., p. 253. 



Definition. Thalassicollida without extracapsular alveoles, but with large 

 roundish or globular alveoles within the central capsule, with a simple spherical, not 

 branched nucleus in the centre. 



The genus Thalassolampe is, next to Actissa, the most simple of all Radiolaria, but 

 differs from it by the large intracapsular alveoles. By these the central capsule is inflated 

 to an extraordinary size, which in Thalassolampe maxima exceeds that of most other 

 Radiolaria. From the nearly allied Thalassopila it differs by the simple spherical 

 nucleus, from Physematium by the absence of spicula. Of the two species of the genus 

 the first observed Thalassolampe margarodes, 1862, is Mediterranean, the second, 

 Thalassolampe maxima, 1882, is Indian. 



1. Thalassolampe margarodes, Haeckel. 



Thalassolampe margarodes, Haeckel, 1862, Monogr. d. Eadiol., p. 253, Taf. ii. figs. 4, 5. 

 Thalassolampe margarodes, R. Hertwig, 1876, Histologie d. RadioL, p. 68, Taf. iii. figs. 1-5. 



Spherical body very soft and limpid, somewhat pearl-like opalescent, yellowish or bluish. 

 Central capsule with a very thin structureless membrane, its diameter six to eight tunes as large as 

 that of the central spherical nucleus. Wall of the vesicular nucleus thick, perforated by fine pore- 



1 Thalassolampe = Sea-scum ; 9X*<ra and 



