The shells of this genus are remarkable for their fragility, delicacy,
and elegance; they resemble a scroll, ornamented with various
canaliculated grooves from the summit to the margin, which is
bicarinated. The colour is usually bluish, but the keel is of a darker
hue; they vary greatly in size.
Shell navicular, symmetrical, very thin, compressed, bicarinated,
sub-involuted longitudinally in the same plane; aperture very large,
entire, symmetrical, square in front, slightly modified by the turn of
the summit, and provided on each side with an earlike appendage, with
thick and smooth edges; lips sharp.
Argonauta argo.
A. tuberculosa.
A. nitida.
_A. argo._ The Portuguese man-of-war. Pl. 35, fig. 1.
Characterized above; shell whitish, fragile, keel rather narrow, with
sharp-pointed tuberculations; sides striated transversely, wrinkled
longitudinally.
_A. tuberculosa._ The tuberculated Argonaut. Pl. 35, fig. 2.
Species more convex at the sides, with nodulous elevations; keel
broader, points more obtuse.