204 BULLETIN 17 5, UNITED STATES NATIONAL MUSEUM 



GENERAL CONCLUSIONS 



Six species and thirteen forms may be recognized in the genus 

 Pituophis. Three of these, d. deppei, d. jani, and lineaticollis, form a 

 natural group characterized by the presence of two prefrontals, a 

 broad low rostral, and the entrance of two supralabials into the orbit 

 on each side. The other forms all have four prefrontals and a single 

 supralabial entering the eye on either side, but differ widely in the 

 shape of the rostral plate. The four subspecies of melanoleucus 

 form a natural group in the common possession of a very long and 

 narrow rostral, the two subspecies of sayi have a moderately long 

 rostral, longer in s. sayi than in s. ajffinis, and the other three forms, 

 vertebralis and the three subspecies of catenifer, are characterized by 

 a low broad rostral. P. vertehralis, however, must be considered 

 separately from the forms of catenifer since it obviously represents a 

 distinct evolutionary line with an independent origin. 



Thus, two major groups are distinguishable, the latter of which 

 may be further subdivided into four minor groups, as follows: 



(deppei deppei. 

 deppei jani. 

 lineaticollis. 



melanoleucus melanoleucus. 

 melanoleucus mugiius. 

 melanoleucus lodingi. 

 melanoleucus ruthveni. 



sayi group. 



sayi sayi. 

 sayi affinis. 



catenifer catenifer. 

 catenifer deserticola. 

 catenifer annectens. 



vertehralis. 



The variation found to occur in the genus has been discussed in 

 detail, in the description of the genus as a whole, as well as in the 

 discussions of the various forms. The main conclusions in regard to 

 variational tendencies in the genus may be summarized here as follows: 



1. Three types of variation are found to exist — individual, sexual, 

 and geographic. 



2. The most striking variation is individual, and most of the charac- 

 ters show an extremely wide range of variation not only for the 

 genus as a whole, but in each separate form as well. 



3. Sexual variation is marked in several characters. Scale rows 

 and ventrals are consistently higher in females throughout the genus, 

 while caudals, the proportionate tail length, and the number of tail 

 spots are universally higher in males. No other tendencies in sexual 

 variation are consistent for the genus. 



