Range, 4300 ft., 1.

N. a. leucodon, 46 specimens (in Mus. Nat. Hist., Univ. Kansas, unless otherwise noted) from: SAN LUIS POTOSI: 6 km. S Matehuala, 13 (LSU); 1 km. S Matehuala, 2 (LSU); 7 km. W Presa de Guadalupe, 5 (LSU); Presa de Guadalupe, 4 (LSU); 8 mi. SW Ramos, 6700 ft., 3; 10 mi. NE San Luis Potosí, 6000 ft., 2; San Luis Potosí, 9 (USNM); Hda. La Parada, 8 (USNM).

I am grateful to Prof. E. Raymond Hall and Mr. J. Knox Jones, Jr., for permission to examine critical specimens and for helpful suggestions. I am grateful also to Dr. George H. Lowery, Jr., of the Louisiana State University (LSU) and to Dr. David H. Johnson and Dr. Richard H. Manville of the United States National Museum (USNM) for the loan of specimens. Gerd H. Heinrich (in 1953) and Percy L. Clifton (in 1961) collected for the Museum of Natural History the Tamaulipan specimens herein reported. Fieldwork was supported by the Kansas University Endowment Association. Laboratory phases of the study were made when the author was a half-time Research Assistant supported by grant No. 56 G 103 from the National Science Foundation.

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