Page:Scientific results HMS Challenger vol 18 part 1.djvu/600

392 five, but may amount to nineteen, to twenty-one or more; they lie constantly in pairs on both sides of the equatorial constriction (Pl. 40, figs. 12, 13).

The cortical shell may either remain simple (Ommatocampe, Pl. 40, fig. 10), or become double (Desmocampe, Pl. 40, fig. 12), or sometimes triple (Zygocampe, (Pl. 40, fig. 13). In the latter cases the outer (secondary and tertiary) cortical shells are commonly incomplete, and only developed around the proximal chambers of the complete first (primary) cortical shell, its distal chambers remaining simple.

The Medullary Shell is constantly double, as in the Panartida; its form is either spherical or lenticular, compressed in the direction of the main axis. It is always connected with the equatorial constriction of the cortical shell by a number of radial beams, lying either in the equatorial plane or on each side of it (Pl. 40, figs. 10-13).

The Central Capsule of the Zygartida is constantly cylindrical; its increasing growth on both poles of the axis corresponds to that of the including cortical shell. Commonly (but not always) its cylindrical surface is annulated, with five or more transverse strictures, corresponding to those of the cortical shell. From the inner surface of the latter it is separated by a jelly-mantle, the calymma.

Definition.— with simple cortical shell and double medullary shell, without polar tubes.

The genus Ommatocampe was founded by Ehrenberg in 1860 for one of his "Haliommatina," with the following diagnosis:—"Shell rod-like, long, articulate, with nucleus, without spines, with four or more joints." The species figured by him, Ommatocampe