Page:Scientific results HMS Challenger vol 18 part 1.djvu/563

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Definition.— without peculiar polar appendages (without strong solid spines or hollow fenestrated tubes on the poles of the main axis).

The genus Artiscus represents the most simple and primitive form of the Artiscida, and may therefore be regarded as the ancestral form of this subfamily. It resembles an ordinary double loaf, composed of two equal, nearly ellipsoidal fenestrated shells separated by the stricture in the equatorial plane. Artiscus can be derived from Cenellipsis simply by this equatorial constriction. But it can also be derived from Cyphanta by loss of the medullary shell.

Definition.—Surface of the shell smooth or rough, without radial rods or spines.

1. Artiscus paniscus, n. sp.

Pores of the shell regular, hexagonal, four times as broad as the bars; ten to twelve pores on the half meridian, eight to nine on the half equator. Surface smooth. (The network of this species is quite the same as that of the proximal cameræ of Panartus diploconus, Pl. 40, fig. 1.)

Dimensions.—Main axis of the shell 0.12, equatorial axis 0.07; meshes 0.013, bars 0.003.

Habitat.—Pacific, central area, Station 271, depth 2425.

2. Artiscus facetus, n. sp.

Pores of the shell regular, circular, with prominent hexagonal frame, twice as broad as the bars; twenty-two to twenty-four pores on the half meridian, fourteen to fifteen on the half equator. Surface a little thorny. (The shell of this species exhibits nearly the same formation as that of Cyphonium virgineum, Pl. 39, fig. 12, but without enclosed medullary shells.)

Dimensions.—Main axis of the shell 0.15, equatorial axis 0.09; meshes 0.01, bars 0.005.

Habitat.—Pacific, central area, Station 266, depth 2750 fathoms.

3. Artiscus paniculus, n. sp.

Pores of the shell regular, circular, without hexagonal frame, as broad as the bars; fourteen to sixteen pores on the half meridian, ten to eleven on the half equator. Surface quite smooth.

Dimensions.—Main axis of the shell 0.13, equatorial axis 0.06; meshes 0.01, bars 0.01.

Habitat.—Fossil in the Tertiary rocks of Barbados (Haeckel).