Near-shore deposits of Upper Jurassic age occur along the margin of the former Coahuila Peninsula of northern Mexico and along the site of the Sierra Madre Oriental in eastern Mexico. These deposits contain a mixed bivalve and ammonite fauna whose description will furnish a means of correlation between various facies in the Mexican Geosyncline. Studies of the ammonites, undertaken in the present paper, confirm the validity of most of Burckhardt’s stratigraphic divisions for the off-shore deposits and show that they can be traced into the near-shore deposits. New information concerning the stratigraphic ranges of certain ammonite genera and the discovery of the presence of other genera have made necessary slight changes in Burckhardt’s subdivisions and have shown that the succession of ammonite assemblages in the Upper Jurassic of Mexico agrees fairly well with that of the Mediterranean province.

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