15. A new hylid frog from eastern Mexico. By Edward H. Taylor. Pp. 257-264, 1 figure in text. August 16, 1948.
16. A new extinct emydid turtle from the Lower Pliocene of Oklahoma. By Edwin C. Galbreath. Pp. 265-280, 1 plate. August 16, 1948.
17. Pliocene and Pleistocene records of fossil turtles from western Kansas and Oklahoma. By Edwin C. Galbreath. Pp. 281-284, 1 figure in text. August 16, 1948.
18. A new species of heteromyid rodent from the Middle Oligocene of northeast Colorado with remarks on the skull. By Edwin C. Galbreath. Pp. 285-300, 2 plates. August 16, 1948.
19. Speciation in the Brazilian spiny rats (Genus Proechimys, Family Echimyidae). By João Moojen. Pp. 301-406, 140 figures in text. December 10, 1948.
20. Three new beavers from Utah. By Stephen D. Durrant and Harold S. Crane. Pp. 407-417, 7 figures in text. December 24, 1948.
21. Two new meadow mice from Michoacán, México. By E. Raymond Hall. Pp. 423-427, 6 figures in text. December 24, 1948.
22. An annotated check list of the mammals of Michoacán, México. By E. Raymond Hall and Bernardo Villa-R. Pp. 431-472, 2 plates, 1 figure in text. December 27, 1949.
23. Subspeciation in the kangaroo rat, Dipodomys ordii. By Henry W. Setzer. Pp. 423-573, 27 figures in text, 7 tables. December 27, 1949.
24. Geographic range of hooded skunk, Mephitis macroura, with description of a new subspecies from Mexico. By E. Raymond Hall and Walter W. Dalquest. Pp. 575-580, 1 figure in text. January 20, 1950.