Whittock, Nathaniel: The Art Of Drawing And Colouring From Nature, Flowers, Fruit, And Shells: To Which Is Added, Correct Directions For Preparing The Most Brilliant Colours For Painting On Velvet, With The Mode Of Using Them, Also The New Method Of Oriental Tinting ; With Plain And Coloured Drawings (London, 1829)

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which lie adjacent to the north and south pole, the coldness os the
temperature seems to operate in reducing the size os animals, and os
shell-fish particularly. The largest shell at present known is the
chama gigantea, a bivalve, about three feet in length and one soot and
a half in breadth ; the shell itsels being four or five inches thick.'
The two shells forming the subject os this lesson are specimens
of univalve and bivalve. The large shell is cone-shaped, and is
classed by naturalists under the genus conis. The small shell is
bivalve. One side of the shell is here shewn ; it opens like a cockle or
an oyster.
The outline of the large shell will be easily drawn. The inside and
the colouring of the light part of the shell towards the mouth are the
beautiful changing prismatic colours, so difficult to express in paint-
ing, but may be executed to look very well by commencing at the edge
with a light tint of yellow ochre; while this is wet a line with the
large brush, filled with a tint of lake, should be drawn close to the
eds;e of the yellow, and another with a light tint os blue near the edge
of the lake, and close to the blue a thin wash os gamboge. These
colours, softened one into the other with a clean large brush and clear
water, will produce something as near the esfect required as it is pos-
sible to produce on paper. The dark parts of the shell are tinted with
burnt sienna, and the dappling is lake, dragon's blood, and burnt
sienna; the darkest touches are vandyke brown.