SNAKES OF THE GENUS PITUOPHIS 125 



always more than 40 median dark spots on body and tail, which are 

 in marked contrast with the light ground color throughout the body 

 length; in m. melanoleucus there are less than 40 dorsal spots; in m. 

 mugitus the anterior spots are generally blended with the brown 

 ground, but the spots, when distinguishable, number less than 40; in 

 lodingi the dorsum is uniformly black; and in ruthveni the dorsum is 

 brown with 50 darker brown spots, of which the anterior ones are more 

 or less indistinct. 



From the forms of the deppei group, affinis may be distinguished 

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

 entrance of a single supralabial into the orbit on each side, instead of 

 two, and by the longer rostral. 



The longer rostral also distinguishes affinis from vertebralis, which 

 has the rostral always at least as broad as long. From the subspecies 

 of catenifer, affinis may be distinguished by the longer rostral, which 

 (except rarely in deserticola) is never longer than broad in the forms 

 of catenifer. It may be distinguished from these forms also by the 

 pattern. Thus in affinis the dorsal spots number 43 to 86 (average 

 59.5) on body and tail, the posterior ones are generally reddish and 

 always more or less saddle-shaped, and central black spots are lacking 

 on the light scales of the interspaces; in c. deserticola the dorsal spots 

 number 57 to 95 (average 72.9), are never reddish or saddle-shaped, 

 and small central black spots are frequently present on the light scales 

 of interspaces and sides, particularly on the anterior part of the body; 

 in c. catenifer the dorsal spots number 58 to 125 (average 87.3) and are 

 never reddish or saddle-shaped; and in c. annectens the dorsal spots 

 number 69 to 129 (average 99.7) and are never reddish or saddle- 

 shaped. 



From s. sayi, affinis may be distinguished by the shorter rostral, 

 which is only slightly longer than broad, while it is nearly twice as 

 long as broad in s. sayi. Furthermore, in sayi the spots are quad- 

 rangular or bar-shaped and never saddle-shaped or reddish, as in 

 affinis. 



Description. — The body is rather stout, and the snout is neither 

 blunt nor pointed but moderately rounded. The tail forms from 

 0.111 to 0.152 (average 0.132) of the total length. The longest speci- 

 men examined was 1,880 mm. long. 



The dorsal scale formula varies from 25-28-20 to 31-35-25. The 

 number of scale rows at the neck is 25 to 33, most often 29; the maxi- 

 mum number in the middle of the body 28 to 35, usually 31 ; the mini- 

 mum number anterior to the vent 20 to 25, usually 23. The remaining 

 scutellation is as follows: Ventrals 215 to 260 (average 233.1); caudals 

 51 to 71 (average 61.0); supralabials 8 or 9, with the fourth, fifth, or 

 none entering the eye; infralabials 11 to 15, usually 12 or 13; preocu- 

 lars 1 to 3, usually single; postoculars 2 to 6, usually 3 or 4; loreal 



