REVISION OF THE KING SNAKES. 



13 



FiQ. 6.- 



lampropeltia pyrrhomelaena. about 2 x nat. 

 Showing an extra labial in each series. 



A study of the whole genus indicates most strongly that the 

 primitive scale formula is 23-21-19. This and its simple derivative, 

 21-23-21-19, is characteristic of those forms of the two most wide- 

 spread and diversified groups (triangulum and getulus) which show, 

 in other structural 

 features, the most 

 primitive condition. 

 Higher and lower for- 

 mulae in the genus 

 Lampropeltis are be- 

 lieved to indicate spe- 

 cialization, or depar- 

 ture from the original stock of the genus. 



Variation in labials. — -Both upper and lower labial series are 

 remarkably constant throughout the genus. The supralabials are 

 normally seven (fig. 3), but in very rare instances this number is 



reduced to six by a fusion 

 of the sixth with the fifth. 

 Variation to eight occurs 

 occasionally in many 

 forms and in a few 

 (calligaster, pyrrhomelae- 

 na) it is rather common. 

 In all cases the presence 

 of eight supralabials is 

 due to the interpolation 

 4, 5, and 6), or to the 



Fig. 6.— Lampropeltis calligaster (Univ. Mich. no. 44973). 

 li X NAT. SIZE. Showing position of the added labial in 

 each series. 



of a scute between second and third (figs 

 division of the second. 



The infralabials are more variable. Normally there are nine 

 (fig. 3), but in a few forms ten is common or usual (conjuncta, pyrr- 

 homelacna, calligaster, Jloridana, mexi- 

 cana, altema), and in a few others eight 

 is common or usual (micropholis, rJiom- 

 homacvlata, elapsoides, virginiana) ; those 

 that commonly have eight may rarely 

 have seven, and those that commonly 

 have ten may occasionally have eleven. 

 Reduction from nine to eight takes 

 place in the great majority of cases by 

 reduction of the seventh and its fusion with the eighth (fig. 7); in 

 some instances it seems to occur by loss of the ninth. The method 

 of increase to ten is less constant. Since this is commonly accom- 

 panied by increase to eight in the upper series, and since the latter 

 is due to the addition of a scute in front of the eye, it is most natural 

 to expect that the tenth lower labial would also be inserted in front 



Fig. v.— Lampropeltis elapsoides elap- 

 soides (U.S.N.M. no. 28910). 2 X NAT. 

 size. Showing reduction of lower 

 lablals from 9 to 8. 



