Definitions for "Doublure"
The reflexed margin of the trilobite carapace.
reflexed continuation of dorsal exoskeleton onto ventral surface, typically as a ventral cephalic and/or pygidial rim
shell continuation under the trilobite, typically as a ventral cephalic, thoracic, and/or pygidial rim.
The lining of a book cover, esp. one of unusual sort, as of tooled leather, painted vellum, rich brocade, or the like.
The interior lining of a book in silk or leather etc rather than paper
The paste-downs being of leather, not paper.