Osentsoir
France, 4e quart du XVe siécle.
Cuivre doré, émaux translucides sur basse-taille, verre
Fonds Du Sommerand, Cl. 992

Which can be roughly translated as:

Monstrance
France, 4th quarter of the 15th Century.
Gilded coper, translucent enamel "basse-taille", glass.
Funds from Sommerand, Cluny catalog number 992

Another view of the previous object

More information on reliquaries can be found at Wikipedia and at the Metropolitan Museum of Art site.