-------+------+------+-----+------+-----+-----+----+-----+----+---- 9 mean| 198.7| 96 | 22 | 93.4| 28.1| 14.0| 4.4| 11.2| 6.0| 4.5 max.| 205 | 105 | 22 | 105.0| 28.7| 14.2| 4.6| 11.7| 6.4| 4.6 min.| 187 | 90 | 22 | 85.7| 27.3| 13.4| 4.3| 10.6| 5.7| 4.3 -------+------+------+-----+------+-----+-----+----+-----+----+---- 11 mi. W, 8 mi. S Piedra, Tamaulipas -------+------+------+-----+------+-----+-----+----+-----+----+---- 5 mean| 201.8| 101.8| 22.6| 101.8| 28.5| 14.0| 4.4| 11.3| 6.1| 4.3 max.| 214 | 110 | 23 | 109.3| 29.0| 14.1| 4.6| 11.5| 6.2| 4.7 min.| 193 | 94 | 22 | 94.9| 28.2| 13.9| 4.2| 11.0| 6.0| 4.1 -------+------+------+-----+------+-----+-----+----+-----+----+---- _P. boylii ambiguus_ La Vegonia, Tamaulipas -------+------+------+-----+------+-----+-----+----+-----+----+---- 7 mean| 199.1| 101.6| 21.3| 104.3| 26.9| 13.4| 4.3| 10.5| 5.6| 4.3 max.| 213 | 109 | 22.4| 108.9| 28.6| 13.7| 4.5| 11.8| 5.9| 4.7 min.| 188 | 97 | 20 | 98.0| 26.4| 13.2| 4.2| 9.5| 5.3| 4.1 -------+------+------+-----+------+-----+-----+----+-----+----+---- Monterrey, Nuevo León -------+------+------+-----+------+-----+-----+----+-----+----+---- 16 mean| 199.7| 103.2| 21.3| 106.9| 27.6| 13.9| 4.4| 10.7| 5.6| 4.2 max.| 216 | 114 | 22 | 125.6| 28.2| 14.9| 4.6| 11.5| 5.8| 4.5 min.| 176 | 92 | 19 | 88.0| 26.8| 13.2| 4.1| 10.2| 5.0| 4.0 -------+------+------+-----+------+-----+-----+----+-----+----+---- _Specimens examined._--Total 64 as follows: NUEVO LEON (USNM): Monterrey, 37; _Cerro de la Silla_, 18. COAHUILA: 12 km. E San Antonio de las Alazanas, 9000 ft., 2. TAMAULIPAS: La Vegonia, Sierra San Carlos, 7 (UMMZ). I am grateful to the following persons for the loan of specimens: G. B. Corbet, British Museum, Natural History (BM); David H. Johnson, United States National Museum (USNM); George H. Lowery, Jr., Louisiana State University (LSU); Philip Hershkovitz, Chicago Natural History Museum (CM); William B. Davis, Texas Agricultural and Mechanical College (TAM); W. H. Burt and Emmet T. Hooper, University of Michigan Museum of Zoology (UMMZ). Specimens lacking designation as to collection are housed in the Museum of Natural History of The University of Kansas. I am indebted to Professor E. Raymond Hall and Mr. J. Knox Jones, Jr. for the use of these specimens and for other assistance. It is appropriate to record also that the findings reported above are an outgrowth of related work done as a Research Assistant under Grant No. 56 G 103 from the National Science Foundation. LITERATURE CITED DALQUEST, W. W. 1953. Mammals of the Mexican state of San Luis Potosí. Louisiana State Univ. Biol. Sci. Ser., 1:1-233, December 28. HALL, E. R., and KELSON, K. R. 1959. The mammals of North America. The Ronald Press, New York, vol. 2:ix + 547-1083 + 79, illustrated, March 31.