Now, leaving the animal, though we might devote a few moments to the
admiration of its rich colours, adorned as is its deep yellow hue with
lines and clouds of deeper brown, let us look at the shell, the solid
house of stone, which our friend Trochus has himself built up to cover
his head in the hour of danger. How well has he combined the _utile cum
dulci_!--the comfortable with the ornamental! Its general form is that
of a cone of much regularity, but with an oblique base, and perhaps
you may be surprised to learn that this conical form is but the result
of the winding of a very long cone upon itself in a spire. But if you
examine a dead shell with care, you will see that it is so. Supposing
you had a very long and slender hollow cone of plastic material, and,
beginning with the acute point, you twined the whole upon itself,
descending in a spiral form, you would have the representation of a
turbinate shell, which, by a little gentle pressure of the fingers,
might be moulded, without at all losing its essential character, into
the exact shape of our Trochus, in which the progress of the spire
can without difficulty be followed as well by slight inequalities of
surface as by the arrangement of the colours.
It is one of our showy shells. This specimen before us has for its
ground colour a chaste, cool grey, occasionally varied with tints of
reddish buff, but most conspicuously adorned with a series of large and
regular spots of purplish crimson running along the lower angle of the
spire from the base to the summit. Each of these spots passes off into
an oblique line above, the repetition of which augments the beauty of
the pattern.
The interior of the shell has a glory of quite another character. It
is covered with a coat of nacre or pearl, of exceedingly brilliant
and rich lustre, and the presence of this inward pearliness is quite
characteristic of this genus, and of most of the others belonging to
the same family, the _Turbinidæ_. Many of the fine large tropical
species are specially conspicuous for this adornment, as I have seen
in those that lie along the dazzling beach of coral-sand in lovely
Jamaica. The pearl of these shells is used in the arts. De Montfort
mentions a necklace which he had seen, that was made out of the nacred
part of the shell of the _Turbo smaragdus_, and which was _much more
brilliant and beautiful_ than any of the finest orient pearls.[3]
And Chenu observes:--“Les grandes espèces fournissent une fort belle
nacre, employée pour les ouvrages de marqueterie. Quelques espèces
ont reçu des noms sous lesquels les marchands les distinguent: il y
a le Burgau ou Nacré; la Veuve Perlée, dont les tubercles extérieurs
usés ressemblent à des perles; la Bouche-d’Or, dont la nacre est d’un
beau jaune doré; la Bouche-d’Argent; le Perroquet, ou Turbo Impérial,”
etc.[4]
At another time we may examine the structure of shell, and inquire by
what instruments and with what materials the ingenious animal contrives
to construct so strong and so elegant a dwelling. For the present,
however, as the month is January, we shall, if we sit still longer, run
the risk of “catching a cold,” if we catch nothing else, though the
wind _is_ in the south, and the temperature is so mild for the season.