Here are some pictures of a nicely preserved french clasp knife that is a "jambette dit flatin".  This one was found in France in a village called Saint-Euphemie 50 km from Lyon.  It was discovered between two walls of a very old 200-300 year old house when renovations were underway to widen a door.

The blade is stamped M.DEVILLE in a cartouche like pattern with decorative ends.  There are references to the Deville family in Saint-Etienne  working in the first half of the 18th century in Jean Jacques Buigné, Le "QUI EST QUI " de l'arme en France - de 1350 à 1970, Éditions du Portail, 2001.  The blade was unquestionably manufactured in Saint-Etienne.

Length of blade : 10cm,

Length of handle : 11 cm

Handle appears to be boxwood. 

It is interesting to note that the knife`s handle does not appear to be the original but rather a crude hand-made later addition.

These knives are typical of the ones used here in north america for the Indian trade under the french regime.

First half of the 18th century.