SNAKES OF THE GENUS PITUOPHIS 169 



oftenest 8, with the fourth, fifth, or none entermg the eye; infralabials 

 9 to 15, most commonly 12 or 13; preoculars 1 or 2; postoculars 2 to 

 6, usually 3 or 4; loreal usually present, occasionally spHt to form 

 two or even three small scales; one or more azygos plates present 

 between the prefrontal and preocular in about 25 percent of the speci- 

 mens examined and occasionally one present between the prefrontal 

 and preocular on either side, or between prefrontals and intemasal on 

 each side; rostral plate generally as broad as long but occasionally 

 very slightly longer than broad, penetrating from one-third to all the 

 distance between the internasals; frontal usually undivided but 

 rarely split for as much as one-third of its length. 



The dentition is as follows: Mandibular teeth 16 to 22, decreasing 

 slightly in size posteriorly ; maxillary teeth 14 to 17, decreasing slightly 

 in size posteriorly; palatines 9 to 11, sHghtly smaller than the man- 

 dibular and maxillary teeth; pterygoids 7 to 13, shghtly smaller than 

 the palatines, and decreasing slightly in size posteriorly. 



The dorsum bears a series of median quadrangular spots, which are 

 black, dark brown, or grey-brown and number 43 to 74 (average 56.6) 

 on the body and 11 to 22 (average 16.2) on the tail. These spots are 2 

 to 6 scales each in length and 8 to 12 scales in width and are separated 

 by interspaces of 1 to 4 scales. There are two or three rows of smaller 

 spots on each side, of which the uppermost are the most distinct and 

 the largest. The lightest spots of both dorsal and lateral series are 

 more or less outlined in black. The Ught scales of the sides and inter- 

 spaces frequently bear each a small central black spot, at least on 

 the anterior part of the body. The ground color of both dorsum and 

 belly is a yellowish white. The belly bears a series of lateral spots 

 on each side, which are each 1 or 2 scutes in length and are separated 

 by 1 to 3 scutes. The middle of the belly may be immaculate or 

 irregularly spotted with small dark spots throughout or on the posterior 

 half only. The top of the head is grey or pale brown, more or less 

 mottled with black or dark brown. Dark streaks are commonly 

 present from the eye to the posterior angle of the jaw on either side, 

 and transversely across the top of the head, including the posterior 

 halves of the prefrontals, the anterior halves of frontal and supra- 

 oculars, the upper part of the preocular, and the supralabials lying 

 just below the eye. Dark streaks often mark the sutures between 

 the supralabials and the infralabials. The throat is white. (Fig. 64, a.) 



Variation. — In the study of geographic variation the range of the 

 form has been divided into regions from south to north, which are 

 numbered along the abscissas of the accompanying graphs as follows: 



Region 1. Imperial, Riverside, and San Bernardino Counties, Calif., and the 

 southern part of Clark County, Nev. 

 2. Kern, Fresno, Tulare, Inyo, and Mono Counties, Calif.; the northern 

 part of Clark County, Nev., and Washington County, Utah. 



