_Cnemidophorus sacki zweifeli_, 207 specimens, as follows: _Michoacán_: Apatzingán, CNHM 36966-8, 38969, 38971 (18), 38972 (50), UIMNH 36772-7, USNM 135967-8, 135970, 135972-3; 4 km. E of Apatzingán, UMMZ 85412; 6.5 km. E of Apatzingán, UMMZ 114731 (5); 5 km. W of Apatzingán, KU 29289-90, 29293-7; 10 km. W of Apatzingán, UMMZ 114730 (4); 12.3 km. S of Apatzingán, UMMZ 112647; 16 km. S of Apatzingán, KU 29298; 14 km. SSW of Apatzingán, KU 29735, 29746, 29750-2; 10 km. W of Buenavista, UMMZ 114719 (3); Capirio, UMMZ 112643, 114722 (2), 114733, 119536-50; 4 km. N of Capirio, UMMZ 112644 (3), 112645; 5.6 km. N of Capirio, UMMZ 114732; 2 km. S of Charapendo, UMMZ 112639 (12); Chinapa, UMMZ 119556 (2); Jazmin, UMMZ 114725 (2); between La Playa and Volcán Jorullo, UMMZ 104748 (2); Limoncito, UMMZ 119552 (3); 14 km. S of Lombardia, KU 29299-301, 29303, 29305-11; 6 km. SW of Nueva Italia, UMMZ 112640 (2); 2.7 km. S of Nueva Italia, UMMZ 112641 (4); 5 km. N of Nueva Italia, UMMZ 114721; Río Marquez, 10 km. S of Lombardia, UMMZ 112642, 112646; Río Marquez, 13 km. SE of Nueva Italia, UMMZ 114726; 6 km. N of Tafetan, UMMZ 119555 (18); 14.5 km. E of Tepalcatepec, UMMZ 114720 (2); 6 km. S of Tzitzio, UMMZ 99199, 99200 (2); 19 km. S of Tzitzio, UMMZ 99154; Volcán Jorullo, UMMZ 104449 (4), 104750; Ziracuaretiro, UMMZ 114724; 3 km. NW of Zirimicuaro, UMMZ 114723. _Acknowledgments._--For the loan of specimens under their care I am indebted to Doris M. Cochran, United States National Museum (USNM); Norman Hartweg, University of Michigan Museum of Zoology (UMMZ); Robert F. Inger, Chicago Natural History Museum (CNHM); and Hobart M. Smith, University of Illinois Museum of Natural History (UIMNH). I thank Ann S. Duellman, Richard E. Etheridge, Fred G. Thompson, Jerome B. Tulecke, and John Wellman for their assistance in the field, Lorna Cordonnier for the drawing reproduced as Figure 1, and Richard G. Zweifel for helpful suggestions and criticism. Field work in México was made possible by grants from the Penrose Fund of the American Philosophical Society and the Bache Fund of the National Academy of Sciences in co-operation with the Museum of Zoology of the University of Michigan. _Transmitted February 2, 1960._ [] 28-2494 * * * * Transcriber's Notes. This file was derived from scanned images. With the exception of two typographical errors that were corrected, the original text is presented. Figure 1 has the notation ×5 after the caption to let the reader know that the image was enlarged by a factor of five. Typographical Errors Corrected: Page 589, Paragraph 2: Tepalcatapec => Tepalcatepec Page 592, Paragraph 2: ground color => ground-color the hypented versionappearsn Page 596 in the paragraph following the table. Emphasis Notation: _text_ - italicized +text+ - bold ~text~ - small caps