Page:Scientific results HMS Challenger vol 18 part 2.djvu/69

Rh reindeer. If the lateral ends of the branches of this species become united in the frontal plane, we get Microcubus, the four upper spines forming the mitral ring, the four middle the equatorial ring, and the four lower the basal ring.

Dimensions.—Diameter of the gate 0.08; length of the spines 0.09.

Habitat.—Central Pacific, Station 272, surface.

7. Lithocircus furcatus, n. sp.

Gate ovate. Ring ovate, with three sharp prominent edges. The two lateral edges are smooth. The median edge (in the sagittal plane) bears sixteen to twenty forked spines (commonly eight dorsal, eight ventral, and four basal). All the spines are of nearly equal size, slightly curved, and about half as long as the short sagittal axis of the ring.

Dimensions.—Diameter of the gate 0.08 to 0.12; length of the spines 0.03 to 0.04.

Habitat.—North Pacific, Station 253, depth 3125 fathoms.

8. Lithocircus magnificus, n. sp. (Pl. 81, fig. 16).

Gate ovate or nearly elliptical. Ring ovate, with three prominent edges, and numerous richly branched spines arising from the three edges. The specimen figured, which I observed living in the Mediterranean, exhibited eight bunches of larger spines, three dorsal, three ventral, one apical, and one basal bunch; the latter much larger than the seven others. Each bunch was composed of two to four larger and numerous smaller spines, their branches curved and forked. The ovate purple central capsule, with a distinct podoconus, filled more than the half of the gate.

Dimensions.—Diameter of the gate 0.1 to 0.13; length of the spines 0.05 to 0.15.

Habitat.—Mediterranean (Portofino, 1880), Atlantic (Canary Islands), Station 354, surface.

Definition.— with a simple dipleuric or bilateral ring, smooth or thorny, without branched spines and basal feet.

The genus Zygocircus and the following Dendrocircus differ from the two preceding older genera in the bilaterally symmetrical or dipleuric form of the sagittal ring. Whilst in Archicircus and Lithocircus the two sagittal halves or bows of the ring, the dorsal and ventral bow, are equal (therefore the fundamental form amphithect or diphragmatic), here both bows become distinctly different; the dorsal bow is constantly more straight (often vertical), the ventral bow more convex (obliquely ascending). This dipleuric differentiation is most important, as it is transmitted to the greater number of by heredity.