Page:Scientific results HMS Challenger vol 18 part 1.djvu/903

Rh 5. Lithelius solaris, n. sp. (Pl. 49, fig. 2).

Cortical shell spherical, covered with simple, very numerous (two hundred to three hundred) bristle-shaped radial spines, longer than the diameter of the shell. Spiral turnings double, both of the same breadth, gradually increasing with the growth of the shell and several times surpassing the diameter of the simple spherical medullary shell. (Pl. 49, fig. 2, exhibits only the first convolutions in the centre of the shell.)

Dimensions.—Diameter of the cortical shell (with four spiral convolutions) 0.18; diameter of the medullary shell 0.02.

Habitat.—Pacific, central area, Stations 266 to 272, surface and in various depths.

6. Lithelius arborescens, n. sp.

Cortical shell lentelliptical, one and a half times as long as broad, covered with numerous (fifty to eighty or more) branched radial spines, about as long as the greatest diameter of the shell; each spine with two to four lateral branches, which are again branched or dichotomous. Spiral turnings double, both of little different breadth, which increases considerably with the growth of the shell, so that the third turn is four times as broad as the simple spherical medullary shell.

Dimensions.—Length of the cortical shell (with three spiral convolutions) 0.18, breadth 0.12; diameter of the medullary shell 0.01.

Habitat.—North Atlantic, Færöe Channel, surface, John Murray.

Definition.— with double, trizonal, or Larnacilla-shaped medullary shell.

Definition.— with double, trizonal, or Larnacilla-shaped medullary shell; cortical shell subspherical or lentelliptical, constructed of a simple or double spiral of the transverse girdle (or primary cortical girdle); the spiral lamella revolving around the principal axis.

The genus Larcospira begins the interesting series of the Larcospirida, or of those Lithelida in which the medullary shell is formed by a trizonal or Larnacilla-shaped lattice-shell, and the cortical shell by spiral turnings of one of the three girdles, which compose the cortical shell of the Pylonida. In Larcospira, as the oldest and most simple form of Larcospirida, the spiral is formed by the transverse girdle, or the first girdle of the Diplozonaria, the only cortical girdle of Amphipyle. If in this genus one of both wings of the transverse girdle grow stronger than the other and overgrow the latter, turning