Page:Scientific results HMS Challenger vol 18 part 2.djvu/67

Rh 12. Archicircus triglyphus, n. sp.

Gate ovate. Ring hexagonal, with three prominent edges and twenty-two to twenty-four simple curved spines, arising from the six corners and about as long as the diameter of the gate. In the basal corner arise six to nine larger spines, protecting the basal pole of the central capsule. From each of the five other corners arise three spines, diverging from the three edges.

Dimensions.—Diameter of the gate 0.07 to 0.11; thickness of the ring 0.008 to 0.011.

Habitat.—Central Pacific, Station 268, depth 2900 fathoms.

13. Archicircus sexangularis, n. sp. (Pl. 81, fig. 12).

Gate hexagonal or subcircular. Ring hexagonal, with two sharp prominent edges and six pairs of divergent spines, about as long as the radius of the gate, and arising from the two edges at the six corners. The two apical and the two basal spines are simple and conical, whilst the eight other spines, arising in pairs from the two dorsal and the two ventral corners, are slightly forked.

Dimensions.—Diameter of the gate 0.06 to 0.08; thickness of the ring 0.01 to 0.015.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms.

Definition.— with a simple amphithect or diphragmatic ring, armed with branched spines, without typical basal feet.

The genus Lithocircus is the oldest known form of all, founded by J. Müller in 1856 for his Lithocircus annularis, the first species of this suborder described. We retain here this cosmopolitan form as the typical representative of the genus, which differs from the preceding Archicircus, its ancestral form, in the development of branched radial spines.

1. Lithocircus annularis, J. Müller.

Lithocircus annularis, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 29, Taf. i. fig. 1.

Gate circular. Ring circular, with four forked or simply branched spines, opposite in pairs in two diameters, perpendicular one to the other. Spines with slender curved fork-branches, about as long as the diameter of the gate. The specimen figured by J. Müller bears a supernumerary fifth spine; numerous other specimens observed by me exhibited a regular cross of four spines.

Dimensions.—Diameter of the gate 0.1 to 0.15; length of the spines 0.01 to 0.18.

Habitat.—Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, surface.