Page:Scientific results HMS Challenger vol 18 part 2.djvu/136

1012 3. Lithocubus vinculatus, Haeckel.

Acanthodesmia vinculata, J. Müller, 1856 (partim), Abhandl. d. k. Akad. d. Wiss. Berlin, Taf. i. fig. 7 (not 4-6).

The twelve rods of the cubical shell are curved and armed with scattered, simple, short spines. The figure 7 of Johannes Müller (loc. cit.) corresponds exactly to the Mediterranean form observed by me at Portofino, and is quite different from his true Acanthodesmia vinculata (loc. cit., figs. 4-6), so that I have no doubt he did observe these two different species (compare above, p. 975).

Dimensions.—Diameter of the cube 0.07; length of the spines 0.02.

Habitat.—Mediterranean (Nice, Portofino).

4. Lithocubus astragalus, n. sp. (Pl. 82, fig. 12).

The twelve rods of the cubical shell are stout and slightly curved, armed with numerous, simple, and irregularly branched spines. Eight larger spines, branched like a deer's antler, arise from the eight corners of the cube.

Dimensions.—Diameter of the cube 0.1 to 0.12; length of the corner spines 0.05 to 0.08.

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

Definition.— with two simple different horizontal rings, connected by numerous (six to eight or more) divergent columellæ.

The genus Circotympanum comprises those Tympanida in which two simple horizontal rings of different size (an upper smaller "mitral ring," and a lower larger "basal ring") are connected by a variable number of divergent rods or columellæ (at least six or eight). Circotympanum is probably derived from Tympaniscus or Tympanidium by partial reduction of the sagittal ring, the upper (apical) and lower (basal) part of which is lost. The geometrical fundamental form is a truncated pyramid with six to eight or more edges.

1. Circotympanum hexagonium, n. sp.

Mitral and basal ring hexagonal, the latter twice as broad as the former, each with a simple small spine on the six corners. Six columellæ nearly straight, as long as the radius of the basal ring. All rods with three prominent edges.

Dimensions.—Breadth of the mitral ring 0.06, of the basal ring 0.11.

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