The specimens from the Sierra San Carlos, Tamaulipas, closely resemble levipes in color, but are referred to ambiguus on the basis of small size, as also are the two specimens from 12 km. E San Antonio de las Alazanas, Coahuila.
Table 1. Measurements (in Millimeters) of Peromyscus
| Number of specimens | Total length | Length of tail-vertebrae | Length of hind foot | Per cent length of tail to head and body | Greatest length of skull | Zygomatic breadth | Interorbital constriction | Length of nasals | Palatine slits | Maxillary tooth-row |
|---|---|---|---|---|---|---|---|---|---|---|
| P. aztecus Mirador, Veracruz | ||||||||||
| 7 mean | 229 | 113 | 24.5 | ... | 30.1 | 15.3 | 4.7 | 12.5 | 6.4 | 4.8 |
| max. | 238 | 121 | 26.0 | ... | 30.9 | 15.8 | 5.0 | 13.5 | 6.8 | 5.0 |
| min. | 215 | 107 | 24.0 | ... | 29.2 | 14.9 | 4.6 | 11.2 | 5.7 | 4.7 |
| P. boylii beatae Las Vigas to 3 km. E thereof, Veracruz | ||||||||||
| 14 mean | 219.3 | 116.7 | 23.8 | 113.7 | 28.9 | 14.4 | 4.5 | 11.5 | 6.3 | 4.5 |
| max. | 235.0 | 130.0 | 25.0 | 128.9 | 29.8 | 15.1 | 4.7 | 12.5 | 6.8 | 4.8 |
| min. | 204.0 | 107.0 | 22.0 | 100.0 | 27.9 | 13.8 | 4.2 | 10.7 | 5.9 | 4.4 |
| 6 km. SSE Altotonga, Veracruz | ||||||||||
| 5 mean | 224.4 | 116.1 | 24.1 | 109.4 | 29.1 | 14.5 | 4.5 | 11.6 | 6.4 | 4.5 |
| max. | 241.0 | 126.0 | 25.0 | 114.8 | 30.1 | 15.2 | 4.6 | 12.0 | 6.7 | 4.7 |
| min. | 221.0 | 110.0 | 24.0 | 100.0 | 28.6 | 14.0 | 4.4 | 11.2 | 6.0 | 4.3 |
| P. boylii levipes 3 km. SW San Isidro, San Luis Potosí | ||||||||||
| 11 mean | 205.6 | 99.5 | 22.4 | 93.8 | 28.5 | 14.2 | 4.4 | 11.3 | 5.9 | 4.4 |
| max. | 219.0 | 114.0 | 23.0 | 108.6 | 30.5 | 14.5 | 4.6 | 12.2 | 6.4 | 4.6 |
| min. | 193.0 | 90.0 | 21.0 | 87.4 | 27.2 | 13.8 | 4.2 | 10.8 | 5.6 | 4.1 |
| 6 km. NE Cd. del Maíz, San Luis Potosí | ||||||||||
| 9 mean | 198.7 | 96 | 22 | 93.4 | 28.1 | 14.0 | 4.4 | 11.2 | 6.0 | 4.5 |
| max. | 205.0 | 105 | 22 | 105.0 | 28.7 | 14.2 | 4.6 | 11.7 | 6.4 | 4.6 |
| min. | 187.0 | 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. | 214.0 | 110.0 | 23.0 | 109.3 | 29.0 | 14.1 | 4.6 | 11.5 | 6.2 | 4.7 |
| min. | 193.0 | 94.0 | 22.0 | 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. | 213.0 | 109.0 | 22.4 | 108.9 | 28.6 | 13.7 | 4.5 | 11.8 | 5.9 | 4.7 |
| min. | 188.0 | 97.0 | 20.0 | 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. | 216.0 | 114.0 | 22.0 | 125.6 | 28.2 | 14.9 | 4.6 | 11.5 | 5.8 | 4.5 |
| min. | 176.0 | 92.0 | 19.0 | 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.