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



in the following quadrants of the ring. Important as an ancestral type of such spiral and semi- 

 spiral forms as Staurodwtya cruciata (PI. 42, figs. 4, 12, &c.) and Stylodictya davata, Stylodictyu 

 stellata, &c., of Ehrenberg, 1875 (Abhandl. d. k. Akad. d. Wiss. Berlin, Taf. xxiii. figs. 2, 7, 8, 9). 



Dimensions. Diameter of the ring O05 to 0'08, of the central chamber 0'06. 



Habitat. South Pacific, Station 295, depth 1500 fathoms. 



Subgenus 4. Pentoniscus, Haeckel. 

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



8. Archidiscus pentoniscus, n. sp. 



Eing pentagonal or nearly circular, regular, connected with the central chamber by five radial 

 beams of equal length and at equal distances (72); therefore all five chambers of the ring of equal 

 size and similar form. (Eesembles the central part of the disk of Pentinastrum asteriscus, 

 PL 44, fig. 2.) 



Dimensions. Diameter of the ring 0'05, of the central chamber 0'015. 



Habitat. North Pacific, Station 244, surface. 



Subgenus 5. Hexoniscus, Haeckel. 

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



9. Archidiscus hexoniscus, n. sp. (PI 48, fig. 10, 10a). 



Eing regular, hexagonal, or nearly circular, connected with the central chamber by six radial 

 beams of equal length and at equal distances (60) ; therefore all six chambers of the same size 

 and form. (Eesembles the central part of the disk of Hexinastrum geryonidum, PL 44, fig. 4.) 



Dimensions. Diameter of the ring 0'06, of the central chamber 0'018. 



Habitat. Central Pacific, Station 271, depth 2425 fathoms. 



10. Archidiscus pyloniscus, 11. sp. (PL 48, figs. 11, lla). 



Eing triangular, connected with the central chamber by six radial beams at alternating distances ; 

 therefore three larger chambers (of looser network) alternate with three smaller chambers (of 

 denser network) ; pores of the former twice to three times as large as those of the latter. This 

 species is of peculiar importance, as an immediate transitional form to the Pylodiscida. If these 

 three larger ring chambers lose their few lattice-beams and so became open gates, we get Triolcne 

 or Triopyle, the original forms of the Pylodiscida. 



Dimensions. Diameter of the ring 0'05, of the central chamber - 015. 



Habitat. Central Pacific, Station 266, depth 2750 fathoms. 



