Page:Scientific results HMS Challenger vol 18 part 2.djvu/633

Rh character. The annular constrictions of the multiarticulate shell and the corresponding internal annular septa are here not separated, and do not lie in parallel, transverse planes (as usually happens), but they are all or partly connected in the form of an ascending spiral, so that the joints are not perfectly separated. An irregularity or asymmetry of growth on the different sides of the shell is probably the cause of this strange, spiral structure.

Definition.—Shell conical, gradually dilating towards the wide open terminal mouth.

1. Spirocyrtis scalaris, n. sp. (Pl. 76, fig. 14).

Shell conical, gradually dilating towards the wide open mouth, with ten to twelve spiral convolutions, which correspond to the same number of short and broad chambers or joints, gradually increasing in breadth; all joints form together a spirally winding staircase. The length or height of the single joints or stairs is about equal, and each bears four or five transverse rows of small, square pores. Cephalis flat, cap-shaped, with two or three short divergent horns.

Dimensions.—Length of the shell (with ten joints or turnings) 0.16, length of each joint (on an average) 0.016; breadth of the third joint 0.04, of the fifth joint 0.07, of the tenth joint 0.1.

Habitat.—Central Pacific, Stations 271 to 274, depth 2350 to 2750 fathoms.

2. Spirocyrtis cornutella, n. sp. (Pl. 76, fig. 13).

Shell conical, gradually dilating towards the wide mouth, similar to the preceding, but differing in the curved axis, and the broader and shorter joints, each of which bears only two or three transverse rows of square pores. The turnings of the staircase are not so sharp, nor so distinct, as in the preceding species. Cephalis with a single short horn.

Dimensions.—Length of the shell (with eight joints) 0.1; breadth of the fourth joint 0.05, of the eighth joint 0.08.

Habitat.—Central Pacific, Station 270, depth 2925 fathoms.

Definition.—Shell ovate, or nearly spindle-shaped, more or less tapering towards the narrower, somewhat constricted mouth.

3. Spirocyrtis holospira, n. sp. (Pl. 76, fig. 16).

Shell subovate, twice as long as broad, without external strictures, but with an internal regularly descending spiral septum, which separates seven to nine broad joints of nearly equal lengths; the