2. Archicircus monostephus, n. sp. (Pl. 83, fig. 17).
Gate circular. Ring circular, with three elegantly denticulate edges (one outer median and two lateral edges). Transverse section of the ring triangular.
Dimensions.—Diameter of the gate 0.06 to 0.08; thickness of the ring 0.01 to 0.008.
Habitat.—Central Pacific, Station 274, depth 2750 fathoms.
3. Archicircus ellipsis, n. sp.
Gate elliptical. Ring elliptical, on the inner margin smooth, on the outer margin with fifteen to twenty equal, short, simple, or slightly forked thorns. Transverse section ovate.
Dimensions.—Diameter of the gate 0.05 to 0.09; thickness of the ring 0.01 to 0.014.
Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms; also fossil in Barbados.
4. Archicircus ovalis, n. sp.
Gate ovate. Ring elliptical, smooth, with three prominent, slightly distorted edges, without thorns; in the transverse section triangular.
Dimensions.—Diameter of the gate 0.08 to 0.12; thickness of the ring 0.006 to 0.009.
Habitat.—Tropical Atlantic, Station 347, depth 2250 fathoms.
5. Archicircus monopylus, n. sp.
Gate ovate. Ring ovate, thorny, with three distorted edges, in the transverse section triangular; surface covered with numerous simple small thorns arising from the three edges.
Dimensions.—Diameter of the gate 0.1 to 0.15; thickness of the ring 0.01 to 0.012.
Habitat.—Indian Ocean (Madagascar), Rabbe, surface.
Subgenus 2. Archistephus, Haeckel.
Definition.—Ring polygonal, with four to six or more prominent corners (and commonly with simple spines arising from the corners).
6. Archicircus quadratus, n. sp.
Gate square. Ring square, with three edges and four short simple pyramidal spines on the four corners, opposite in pairs in two perpendicular diameters. Transverse section triangular.
Dimensions.—Diameter of the gate 0.08; thickness of the ring 0.008.
Habitat.—Central Pacific, Station 265, depth 2900 fathoms.
