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



7. Archicircus rhombus, n. sp. (PL 81, fig. 7). 



Gate rhombic. Eing rhombic, with four promineut edges and four pairs of short, divergent, 

 pyramidal spines on the four corners, arising from the lateral edges of the four rods, about as long 

 as the radius of the gate. 



Dimensions. — Diameter of the gate 0-04 to O'OS; thickness of the ring 0"007 to O'Ol. 



Habitat. — North Pacific, Station 244, depth 2900 fathoms. 



8. Archicircus duodenus, n. sp. 



Gate square or rhombic. Eing rhombic, with three prominent edges and twelve stout and 

 straight pyramidal spines, about as long as the radius of the gate. In each of the four corners are 

 three divergent spines, arising fi-om the three edges of each two meeting rods. 



Dimensions. — Diameter of the gate 0'08 ; thickness of the ring 0'012. 



Habitat. — North Atlantic, surface (Eabbe). 



9. Archicircus primordialis, n. sp. (PI. 81, fig. 1). 



Gate ovate. Eiag hexagonal, with three prominent edges and six short pyramidal thorns at 

 the six corners; the basal thorn is either simple or forked. 



Dimensions. — Diameter of the gate 0'07 ; thickness of the ring O'Ol to 0*015. 

 Habitat. — Central Pacific, Stations 265 to 274, depth 2350 to 2925 fathoms. 



10. Archicircus hexacanthus, n. sp. (PI. 81, fig. 4). 



Gate subregular, hexagonal. Eing hexagonal, with three sharp edges and six equal radial 

 pyramidal spines, arising from the six corners and placed in the plane of the ring, about as long 

 as the diameter of the gate. 



Dimensiom. — Diameter of the gate 0'05 to 0-07 ; thickness of the ring O'Ol. 



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



11. Archicircus hertwigii, Haeckel. 



Lithocircus annularis, R. Hertwig {nan J. Miiller), 1879, Organismus der Radiol., p. 69. 

 Taf. vii. fig. 5. 



Gate hexagonal, with prolonged main axis. Eing hexagonal, with two prominent edges and 

 six pairs of equal, short, conical spines, arising from the two edges of the six rods at the six 

 corners and divergent on each side of the plane of the ring. The basal spine-pau- is doubled, 

 therefore there are in all fourteen spines. 



Dimensions. — Diameter of the gate 0-05 to 0-07 ; thickness of the ring 0-005 to 0-006. 



Habitat. — Mediterranean (Messina), Hertwig, surface. 



