No. 10. — Upper Jurassic and Lower Cretaceous Ammonites of the M alone Mountains, Trans-Pecos Texas By Claude C. Albritton, Jr. INTRODUCTION The Malone Mountains are located in southern Hudspeth County, Texas, and may be found on the Fort Hancock topographic sheet. Since 1890 the marine invertebrate fauna enclosed in the Mesozoic rocks of this small desert range and its satellite hills has attracted the attention of paleontologists and collectors. To date the most compre-hensive account of the paleontology is that of F. W. Cragin (1905, pp. 34-109, Pis. I-XXIX) 1 , who has described many new species from the area. Most of Cragin's specimens were collected about a mile northeast of the Malone Mountains from low, outlying hills known as the Malone Hills. Cragin believed that the entire sedimentary sequence of the Malone Hills and Mountains was of Jurassic age. Accordingly, he named this sequence the Malone formation, correlating it, on the evidence of ammonites, with the Tithonian of Europe. More recently, however, F. L. Kitchin (1926) has suggested that a part of Cragin's Malone formation is of Lower Cretaceous age, and C. L. Baker (1927, p. 11) has cited evidence for the presence of Permian strata in the area. In an attempt to solve the stratigraphical problems of the area, the writer in the summers of 1934 and 1935 made an intensive study of 63 square miles centering around the Malone Hills and Malone Mountains. This survey was supervised by Professor M. P. Billings of Harvard University, and conducted with the able assistance of Messrs. C. C. Albritton, Sr., J. Fred Smith, Jr., and J. D. Boon, Jr. Fossils were collected from some 25 carefully measured sections, so that for the first time it is possible to refer individual species to their precise horizons and thus determine the geological ages of the several formations in the area. The writer's collection includes more than a hundred specimens of ammonites. Careful study of these, under the direction of Professor P. E. Raymond, has shown that thirteen species are represented. Of these, five are new and four have not been previously reported from the area. The abundant material at hand has, in addition, provided significant new data on previously described species. Accordingh', the writer presents in the following paragraphs a complete account of the 'Numbers in parenthesis refer to papers listed in the bibliography.