168 BULLETIN 17 5, UNITED STATES NATIONAL MUSEUM 



Diagnosis. — From the forms of the deppei group deserticola may be 

 readily separated by the presence of four, rather than two, prefrontals 

 and the entrance mto the orbit of a single supraocular on either side, 

 instead of one. The shape of the rostral distinguishes it from all 

 the subspecies of melanoleucus, which have the rostral at least twice 

 as long as broad, and from the two species of sayi, s. sayi with the 

 rostral nearly twice as long as broad and s. affinis with the rostral 

 always slightly longer than broad. In deserticola the rostral is rarely 

 longer than broad and never more than slightly so. From affinis it 

 may be further distinguished by the coloration, since in the latter 

 form the dorsal spots are generally saddle-shaped and reddish in 

 color, at least posteriorly, while in deserticola the spots are never 

 saddle-shaped or reddish. In addition, in deserticola the light scales 

 of interspaces and sides frequently each bear a small central black 

 spot, at least on the anterior part of the body, while such markings 

 are generally absent in affinis. From vertebralis, deserticola may be 

 separated by the pattern. Thus in vertebralis the dorsal spots are 

 black or reddish anteriorly, reddish in the middle of the body, and 

 black on the posterior part of the body and on the tail, and are more 

 or less saddle-shaped throughout, and the interspaces between the 

 spots are frequently orange. In deserticola the spots are more or less 

 uniform in color throughout, are never reddish or saddle-shaped, and 

 the interspaces are never orange. Furthermore the small black spots 

 on the light scales of interspaces and sides, which are usually charac- 

 teristic of deserticola, are lacking in vertebralis. These same markings 

 generally serve to distinguish deserticola from catenifer and annectens. 

 From catenijer, deserticola may be separated also by the higher num- 

 ber of ventral scutes. In deserticola the number varies from 214 to 

 259 but is generally more than 228, and the average number is 236; in 

 catenifer, although the number varies from 206 to 234, it is generally 

 less than 228, and the average number is 220. From annectens, 

 deserticola may be distinguished also by the lower number of spots, 

 which is rarely more than 90 in deserticola and rarely less than 90 

 in annectens. Furthermore, the sum of ventrals and caudals is 

 generally less than 300 in deserticola and rarely so in annectens. 



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

 ately blunt. The tail length varies from 0.115 to 0.166 (average 

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

 1,750 mm. in length. 



The dorsal scale formula varies from 27-29-19 to 33-35-23. The 

 number of rows at the neck is 27 to 33, oftenest 29; the maximum 

 number in the middle of the body 29 to 35, most commonly 31; the 

 minimum number anterior to the vent 19 to 25, usually 21 or 23. 

 The remaining scutellation is as follows: Ventrals 214 to 259 (aver- 

 age 235.9); caudals 54 to 71 (average 62.5); supralabials 8 to 10, 



