048 



NORTH AMERICAN SNAKES COPE. 



The affinities of most of these species may be expressed in the follow 

 ins: diagram: 



Angustirostris. Nigrilatus 



SacTtenii. Saxvrittt. 



Sumichrastii. Infemalis. Aurata 



^Fhenax 



Macrostemma. Froxima 



Radix. Megctiops. 



Cyrp)psis—Chrysocep7icila. 



L eptocephxtlcu 



XuZchrzlatus. ScaZaris. 



The^. sirtalis presents tlie greatest number of points of contact with 

 other species. It also inhabits the region of geologically the greatest 

 age, or that region which has been a dry land area for the longest time. 

 Although large portions of the West of North America were elevated at 

 the close of the cretaceous period, and probably before the genus Eu- 

 tienia was in existence, the ancestors of Eutjienia may be safely believed 

 to have inhabited the area which was laud prior to the cretaceous, so 

 that the descent of Eutienia was rendered possible in the Eastern rather 

 than in the Western half of tbe continent. It is thus rendered proba- 

 ble that Eutmnia sirtalis is nearly the ancestral form. This is also con- 

 firmed by the fact that it is a spotted species; since the unicolor species, 

 as E. saurita have spotted young. 



The geographical distribution of these species may be tabulated as 

 follows, by regions: 



'Probably not a homogeueous district. 



