412 PROCEEDINGS OF THE NATIONAL MUSEUM vol. m 



Remarks. — For comparison with Sigma I have had available not 

 only the counts given in table 8 for imperator, but also 26 others given 

 by Allen, 1933, p. 11 ; Bocourt, 1882, pp. 519-521 ; Boulenger, 1893, p. 

 119; Brown, 1893, p. 429; Gaige, 1936, p. 298; Hartweg and Oliver, 

 1940, p. 19 ; Oliver, 1937, p. 19 ; and Ruthven, 1912, pp. 323-324. With 

 one exception, all these counts are less than 253, my maximum ; this 

 exception is a count of 261 on a specimen from Tehuantepec. This 

 seems aberrant, since it is 9 higher than the 61 other counts available, 

 but in any case there is no doubt that at least an average difference 

 exists between the Tres Marias specimens and those from the main- 

 land. Exclusive of the single aberrant count, those from the main- 

 land vary from 225 (Boulenger) to 253, with an average of 241.6 

 and an interquartile range of 235 to 249. 



CROTALUS ATROX Baird and Girard 



Eleven specimens were secured, as follows : Chihuahua : 7 miles 

 west of Carrizal (No. 104614) ; 4 miles south of Ascencion (No. 

 104625) ; Rio Santa Maria, near Progreso (Nos. 104619-20, 104622-4). 

 Nuevo Leon: 20 km. south of Sabinas Hidalgo (HMS No. 11530). 

 Tamaulipas : Hacienda La Clementina, 4 miles west of Forlon (No. 

 110607) ; 20 to 26 km. south of Nuevo Laredo (Nos. 110608-9). 



The Museum has 14 other Mexican specimens, from Chihuahua: 

 "Chihuahua" (Nos. 14280, 36995) ; Lake Santa Maria (Nos. 46475, 

 46596) ; Santa Cruz (No. 263). Nuevo Leon (No. 1302). San Luis 

 Potosi (No. 46474). Sonora: Camoa (Nos. 46378-9); San Bernar- 

 dino (Nos. 21045-6) ; Colorado River 10 miles south of United States- 

 Mexican border (Nos. 21824-5). Tamaulipas: Soto La Marina (No. 

 37577). 



*CROTALUS BASILISCUS (Cope) 



The Museum has three specimens, including the type (No. 53586) 20 

 from Colima, one (No. 46468) 21 from Yaganiza, San Pablo, Oaxaca, 

 and one (No. 46467) 21 from Oaxaca, Oaxaca. 



CROTALUS DURISSUS DURISSUS Linnaeus 



Five specimens are from La Esperanza, Chiapas (near Escuintla) 

 (Nos. 110613-4) ; Xochicalco, Morelos (No. 110610) ; Las Vacas, 24 km. 

 from Tequexistlan, Oaxaca (No. 110612) ; Paso del Macho, Veracruz 

 (No. 110611). The ventrals and caudals of these specimens, in the 

 above order, are : 172, 32 ( $ ) ; 173, 29 ( $ ) ; 182, — ( ?) ; 182, 25 ( 9 ) ; 

 174, 24 ( 9 ) . In the Oaxaca specimen the neck stripes are only as long 

 as the head ; they are followed after an interval of one scale length by a 



*> Cope, 1864, p. 166. 



** Gloyd, 1940, pp. 142-149, map 10, pi. 16, fig. 1. 



