An elegant, well-known shell, more or less ventricose, discoid, slightly
compressed, umbilicated or not, but never papillose; the septa simple,
transverse, not visible externally, the last deeply sunk and perforated
by a siphon running through them all; edges entire.
The N. Pompilius, when dissected, displays its beautiful pearly
chambers; fine specimens are often converted into drinking-cups by the
Orientals, who sometimes remove the outer coating, so that its whole
appearance is pearly.
The Nautilis varies in size; some are microscopic; and although they
have received different names, and on account of the animal have been
made to form different genera, it was deemed unnecessary to treat of
them here.
Nautilus Pompilius.
Nautilus umbilicatus.
_N. Pompilius._ The Pompilius Nautilus. Pl. 36, fig. 3.
Species not umbilicated; the back rounded; aperture round and pearly;
siphon sub-central; pale yellow, with chestnut streaks and undulations.
_N. umbilicatus._ The umbilicated Pompilius. Pl. 36, fig. 1.
Species umbilicated, sub-orbicular; pale fawn colour, with chestnut
undated transverse clouds.
FAMILY XXII.
HETEROPODA. Two genera.