REPOET ON THE RADIOLARIA. 487 



3. Archidiscus trioniscus, n. sp. 



Eing triangular, roundish, equilateral, connected with the central chamber by three radial beams 

 at equal distances (120); therefore three equal ring chambers. (Resembles the central part of the 

 disk of Tripodictya trigonaria, PL 42, fig. 8, and may be the ancestral form of it.) 



Dimensions. Diameter of the ring 0'04, of the central chamber O014 



Habitat. Central Pacific, Station 265, depth 2900 fathoms. 



4. Archidiscus trithalamus, n. sp. 



Ring irregular, roundish, connected with the central chamber by three radial beams at 

 unequal distances ; therefore three ring chambers of different size. (If these differences be 

 important, they introduce a spiral convolution in the further development of the Porodiscus arising 

 from it.) 



Dimensiom. Diameter of the ring - 06, of the central chamber - 016. 



Habitat. South Pacific, Station 288, surface. 



Subgenus 3. Tetroniscus, Haeckel. 

 Definition. Ring with four chambers, separated by four radial beams. 



5. Archidiscus stauroniscus, n. sp. (PI. 48, figs. 9, 9a). 



Ring regular, square, connected with the central chamber by four radial beams at equal 

 distances, opposite in pairs in two axes perpendicular one to another ; therefore four equal ring 

 chambers (or congruent quadrants of the ring). Resembles the central part of the disk of 

 Staurodictya medusa, &c. (PL 42, figs. 1-3) ; also of Staurodictya gracilis, Ehrenberg, 1875 (Abhandl. 

 d. k. Akad. d. Wiss. Berlin, Taf. xxiii. fig. 3). 



Dimensions. Diameter of the ring 0'05, of the central chamber 0'016. 



Habitat. North Pacific, Station 253, depth 3125 fathoms. 



6. Archidiscus tetroniscus, n. sp. 



Ring elliptical, of rhomboidal fundamental form, connected with the central chamber by four 

 radial beams, halving the sides of the rhombus and opposite in pairs in two axes which are not 

 perpendicular one to another ; therefore four ring chambers in pairs different, two opposite equal and 

 larger than the two others. 



Dimensions. Diameter of the ring O'Oo to 0'07, of the central chamber G'016. 



Habitat. Central Pacific, Station 263, depth 2650 fathoms. 



7. Archidiscus tetrathalamus, n. sp. 



Ring irregular, quadrangular, connected with the central chamber by four radial beams of 

 increasing unequal length ; therefore all four ring chambers of different size, gradually increasing 



