618 Natural History of Molluscous Animals: — 



light from their peculiar surface produced by the curious dis- 

 position of their fibres, and from their semitransparency and 

 form, greatly depends^ on the uniformity of their texture and 

 the colour of the concentric coats of which they are formed^ 

 That their lustre does depend on their radiating fibres, may 

 be distincdy proved by the inequality of the lustre of the 

 ' Colombian pearls,' which are filed out of the thick part 

 near the hinge of the pearl oyster (Avicula margaritifera), so 

 that they are formed, like that shell, of transverse laminae, and 

 they consequently exhibit a plate of lustre on one side which 

 is usually flat, and are surrounded by brilliant concentric 

 zones, which show the places of the other plates, instead of 

 the even, beautiful, soft lustre of the true pearls." 



3. I have, in a former letter [Letter 5., Vol. III. p. 345 — 

 347.1, said as much as seems necessary concerning the colour 

 of shells : but this may be not an improper place to introduce 

 such facts as I have collected relative to the colour of the 

 animals themselves ; for their colours depend on the secretion 

 and deposition of a colouring matter in the mucous coat of 

 the skin. Most shellfish are of a uniform white, a straw, or 

 a greyish colour ; and the dark spots with which they are 

 clouded are almost always occasioned by the opacity of the 

 internal viscera or their contents. There are, however, many 

 -exceptions to this remark ; and these would be still more 

 numerous, were our acquaintance with the inmates of shells 

 more extensive and accurate than it unfortunately is. The 

 animal of our native cowry (Cypr<^'« europee'a) is a most 

 elegant creature [Jig, 107. fl, viewed laterally ; b, from be- 

 107 neath), whose splendid colours are, 



according to my friend Dr. Cold- 

 stream, unrivalled amongst the Gas- 

 teropoda. The proboscis is dark 

 vermilion; the tentacula yellowish 

 red, spotted with yellow ; the upper 

 part of the foot streaked longitudinally 

 with yellow and brown; and the 

 mantle greenish brown, edged with 

 brownish red : but, notwithstanding, the shell is a uni- 

 form dull white. Similar discrepancies between the colour 

 of the shell and its owner are often met with : thus, the 

 Cypr<^'« Voluta of Montagu (Marginella Voluta Fleming) has 

 its fins or lateral expansions elegantly speckled with bright 

 yellow, and the fleshy parts of its body with pink. (Mon- 

 tagu, Test, Brit..^ p. 204.) The long proboscis of the 

 Strombus pes Pelicani luin. is pink, dotted over with milk- 

 white spots ; and the animal of the white Scalaria clathrus is 



