REVISION OF THE KING SNAKES. 



175 



and poor distribution of the material, and, exceptfor pattern charac- 

 ters, b.y the small extent of the range. In the matter of scale rows 

 it should be noted that the common formula is 21-19. In this, and 

 the small percentage of specimens with 17 rows at the end, amaura is 

 like gentilis, and probably like annulata (but the undue proportion 

 of females among the specimens of this form lessens the value of 

 figures based upon characters tliat vary v/ith sex). The infrequent 

 occurrence of a lower formula, as 19-21-19-17, foreshadows a situa- 

 tion that is common in syspila and still more common in triangulum. 

 The distribution of scale formulae between the sexes in amaura is as 

 follows : 



Formula. 



Male. 



Female. 



21-23-21-19 







3 



21-19 



fi 



7 



19-21-19 



3 



1 



19-21-19-17 



3 



1 



19-17 



1 







Thus the formula 21-19 is about as common to one sex as to the 

 other, and may be considered the normal. In accordance with the 

 general rule, the higher formulae are mostly possessed by females, 

 and the lower by males. 



The number of veutrals in the majorit}' of cases lies between 188 

 and 199, therefore averaging a little less than annulata in north- 

 eastern Mexico. With the exception of local variation, this number 

 of ventrals is liardly different from that of syspila and triangvlum. 

 Variation in infralabials and temporals is the same in kind and 

 apparently about the same in frequenc}" as in these same two 

 forms. 



The pattern is rather variable, and to properly interpret this 

 variation many more specimens must be secured. We may say that 

 amaura is characterized by a black head, reddish snout somewhat 

 mottled with darker, and about 22 pairs of black annuli bordering 

 yellow, and separated by red. The latter color may encircle the 

 body or be restricted to wide saddles bordered below with black. 

 Wlien the latter is the case we may have the ventral borders of the 

 saddles near together on the belly, or, at the northern edge of the 

 range, they may be indistinct and only just reach the ventrals. 

 This is a close approach to syspih. When, added to this, there are 

 developed alternating spots near the ends of the ventrals, and the 

 whitish bands have increased to more than 25, and the black of 

 the head has receded or become broken up, then we have syspila. 

 The change to gentilis is not as well shown for lack of specimens, but 

 westward, where the paired black rings increase to more than 25, 



