INTRODUCTION AND ACKNOWLEDGMENTS The strata of the Guadalupe Mountain region can be regarded as the classic Permian of North America. Over 80 years ago these rocks and their fossils were described in some detail, and the first comprehensive report on the marine Permian faunas of North America was based on specimens from the Guadalupe and the Delaware mountains. Furthermore, recent stratigraphic studies in this area have shown that the strata there are particularly significant; as they are transitional in nature, they enable us to correlate the typical marine fossiliferous Permian of the Southwest with contemporaneous beds that are nonfossiliferous. It is the purpose of this report to achieve an understanding of the ammonoid faunas of the Guadalupe Mountain area and to compare and relate these faunas with those found in the well-known Glass Mountain sequence. Naturally, it is impossible to ascertain the full significance of any fauna by a study of specimens from a limited area, and the writers have therefore attempted to take advantage of the rather extensive collections at their disposal. All the Permian ammonoids that have resulted from the recent work of the United States Geological Survey in the Guadalupe Mountain area have been made available to the writers. Also, they have very large collections from the Glass Mountains, which add appreciably to the number of species known from there, and smaller collections from the Sierra Diablo and the Hueco, Finlay, and Chinati mountains of west Texas and from various localities in north-central Texas. . . .