SNAKES OF THE GENUS PITUOPHIS 83 



Diagnosis. — This species may be distinguished from the four sub- 

 species of melanoleucus by the shape of the rostral, wliich is twice as 

 long as broad in the latter forms, while it is always at least as broad 

 as long in vertebralis. From sayi sayi and s. affinis also it may be 

 distinguished by the shorter rostral, since in these forms the rostral 

 is always longer than broad. In addition, the coloration of vertebralis 

 distinguishes it from the two subspecies of sayi and from the three 

 subspecies of catenifer. Thus, in vertebralis the anterior spots arc 

 either black or reddish, the spots in the midregion of the body are 

 always reddish, and the posterior spots are always black; the spots 

 are always more or less saddle-shaped, and the interspaces are a 

 reddish orange. In the subspecies of sayi and catenifer, on the other 

 hand, the spots are more or less uniform in color and are never saddle- 

 shaped except in affinis, and the interspaces are never orange. P. 

 vertebralis may be further distinguished from c. catenijer by the larger 

 number of ventrals (237 to 262 in vertebralis as opposed to 206 to 234 

 in c. catenijer), from c. annectens by the smaller number of spots (48 

 to 81, generally less than 70, in vertebralis, as opposed to 69 to 129, 

 rarely less than 80, in annectens), and from c. deserticola frequently 

 by the maximum number of scale rows, which is oftenest 31 or 29 in 

 deserticola and rarely as low as 31 in vertebralis. From the tliree 

 members of the deppei group vertebralis may readily be separated by 

 the presence of four rather than two prefrontals and by the entrance 

 into the eye on each side of a single supralabial, instead of two. 



Description. — The body is rather slender, and the snout is blunt and 

 somewhat square. The tail length forms from 0.1 10 to 0. 149 (average 

 0.132) of the total length. The longest specimen examined measured 

 1,920 mm. in length. 



The series of specimens available was rather limited, and probably 

 does not represent the full range of variation in the scale characters. 

 As based on the specimens studied, the scutellation may be described 

 as follows: Dorsal scale formula varying from 29-31-23 to 35-35-25; 

 number of rows at the neck 29 to 35, oftenest 31; maximum number 

 in the middle of the body 31 to 35, usually 33; number anterior to 

 the vent 23 to 25, usually 23; ventrals 237 to 262 (average 244.9); 

 caudals 51 to 69 (average 63.4); supralabials 8 to 10, with the fourth, 

 fifth, or sixth, entering the eye; infralabials 11 to 15; preoculars 1 to 3, 

 usually 2 ; postoculars 3 to 5, usually 3 ; loreal always present, occasion- 

 ally divided to form two scales on one or both sides; azygos rarely 

 present between frontal and prefrontals, never between prefrontals 

 and preoculars (present in one specimen between internasals) ; rostral 

 as broad as or broader than long, penetrating never more than one- 

 half, and frequently less, of the distance between the uiternasals; 

 frontal never divided. 



