302 PROCEEDINGS OF THE NATIONAL MUSEUM vol. iie 



row to nearly complete coverage of the first or first and second rows ; 

 for example, one of the three Zuni specimens has yellow limited to 

 a spot on each scale of the first dorsal row, while the others have the 

 first row nearly covered with, and the second row spotted with, 

 yellow (pi. 4). Most Arizona and New Mexico ringnecks show the 

 former condition; most Utah snakes, the latter. In D. p. dugesi the 

 yellow pigment is confined usually to the ventrals, but specimens 

 from Hidalgo (UIMNH 17635), Jalisco (AMNH 3711-12), and 

 Nayarit (AMNH 19724) resemble anteriorly those from Arizona-New 

 Mexico. An individual from Durango, Mexico, (ISM, uncataloged) 

 has faint yellow spots on the first dorsal row and thus appears to be 

 intermediate between D. p. dugesi and D. p. regalis. A similar speci- 

 men from Chihuahua (BYU 14243) has yellow confined to the venter 

 caudad of the neck region. 



The Guadalupe Mountains population (Eddy Co., N. M. -Culberson 

 Co., Tex.) also exhibits intermediacy in coloration as well as certain 

 meristic featm'es described below. One specimen from Walnut 

 Canyon (CCNP 2197) has yellow spots on all scales of the fu'st dorsal 

 row, thus resembling most Arizona-New Mexico ringnecks. Another 

 (CCNP 2201) has such spots only on the anterior quarter of the body, 

 while a third has a uniformly gray dorsum. The McKittrick Canyon 

 snakes have no yellow pigment dorsally except in the region of the 

 partial neck ring, where it reaches approximately the fifth scale row 

 on each side. Restriction of yellow pigmentation to the ventral 

 scales is supposedly typical of D. p. arnyi (Stebbins, 1954, pp. 360, 

 489) as well as D. p. dugesi (Blanchard, 1942, p. 51). 



In southwestern and Mexican Diadophis, the number of labial 

 scales (usually 7/8), loreals (1-1), and pre- and postoculars (2-2) is 

 geogi'aphicaUy stable, although often asymmetrical. By contrast, 

 body length and three of fom* other meristic characters vary clinally 

 (table 10). Two steps in the temporal and dorsal scale row clines are 

 important because they fall at major breaks in the range of nonclinal 

 ventral scale variation (fig, 10). One of these steps occurs in the 

 Guadalupe Mountains south through the Sierra Vie] a and Chisos 

 Mountains, Trans-Pecos, Texas, between the ranges of D. p. arnyi in 

 west Texas and D. p. regalis in central New Mexico. The other lies 

 between the ranges of D. p. regalis in Chihuahua, Alexico, and D. p. 

 dugesi in southern Mexico. The steps are indicated by changes in 

 frequency involving 15-15 and 17-17 dorsal scale rows and 1-1 

 temporals. 



That certain meristic characters exhibit clines in different directions 

 is evident. Ringneck snakes from the Sierra Vieja-Chisos region are 

 closest to D. p. arnyi in dorsal and temporal counts but resemble D. 

 p. regalis in number of ventrals. Almost the opposite situation exists 



