C. Klug, T. Brühwiler, D. Korn, G. Schweigert, A. Brayard & J. Tilsley, London 2007.

   Abstract: Palaeozoic and Mesozoic cephalopod conchs occasionally reveal dark organic coatings at the aperture.
A number of these coatings, including still unrecorded examples, are described, figured and interpreted herein.  On
the basis of elementar analysis, actualistic comparison and a comparison with Triassic bivalves, some of these
coatings are shown to consist of apatite and primarily probably of conchiolin (and also probably melanin). In several
Mesozoic ammonoid genera such as Paranannites, Psiloceras, Lytoceras, Phylloceras, Harpoceras and Chondroceras,
some of these coatings (recorded herein for most of these taxa for the first time) are interpreted as a structure similar to the
black band,which was previously known only from Recent Allonautilus and Nautilus. In contrast to these nautilid genera,
however, the organic material of some Mesozoic ammonoids was not deposited on the inside of the shell but externally,
albeit positioned at the terminal aperture as in Recent nautilids. Some ammonoids of Carboniferous and Triassic age
show several such bands at more or less regular angular distances on the ultimate whorls and at the aperture, e.g.
Nomismoceras, Gatherites, Owenites, Paranannites, Juvenites and Melagathiceratidae gen. et sp. nov.  Triassic
material from Oman shows that the black coating was probably secreted from the inside, because the position of
this organic deposit changes from interior to exterior in an anterior direction (i.e. adaperturally). This structure has
previously been referred to as a 'false colour pattern' and is here interpreted as having been formed at an interim
aperture or megastria ('alter Mundrand').  All structures discussed in the paper are considered to have been secreted
by a single organ and to have been initiated by some form of stress or adverse conditions.  Thus, certain environmental
parameters and growth anomalies appear to have influenced their formation.