118 BULLETIN (31, UNITED STATES NATIONAL MUSEUM. 



Saufifiis (liU'ers from saclceni i)rinfipally in its generally fewer 

 number of lal)ials, subcaudals, and ventral scutes and the shorter tail, 

 and from proximus in the fewer labials and ventral scutes and greater 

 nund)er of subcaudals and slightly longer tail. A comparison of the 

 tables, however, will show that these differences are not sharp. Thus, 

 while the usual number of labials in sackeni are 8/10, the formula 7/10 

 is not rare, while in sauritus the general formula 7/10 is not infre- 

 quently replaced by 8/10. This suggests that the two forms may 

 intergrade in this trait, although the data are not sufficient to establish 

 this geographically. 



It has previousl}^ been noted that proximus specimens from the 

 eastern part of the range show an apparent tendency toward a reduc- 

 tion in the number of supralabials from 8 to 7, the average number 

 for Illinois specimens being almost identical with the average for 

 Indiana specimens of sauritus. Very similar conchtions exist in the 

 case of the other characters. In coastal plain specimens of sauritus 

 the extremes of variation in the number of ventral scutes are quite 

 close to those of saclceni, although the averages are somewhat lower. 

 In southern JNIichigan, Ohio, and Indiana, however, the number of 

 scutes in this series is apparently higher than in either the coastal 

 plain specimens of sauritus or saclceni, which brings the form in this 

 region so close to proximus specimens from Illinois, eastern Iowa, 

 and St. Louis that the character is useless as a distinguishing one. 

 Again, the greater number of subcaudal scutes and the tail length 

 in coastal plain specimens of sauritus approximate the conditions in 

 saclceni, while the shorter tail and fewer subcauchils in western 

 specimens of sauritus are almost identical with eastern specimens of 

 proximus. 



It seems very evident fi'om this digest of the variations in the three 

 forms ( 1 ) that the form sauritus intergrades both with sadcenismd proxi- 

 mus; (2) that the longer tail, more numerous subcaudals, and fewer ven- 

 trals relate the specimens of sauritus fi'om the eastern coastal plain 

 more closely to sackeni, while the shorter tail, few^er subcaudals, and 

 greater number of ventral scutes relate the interior specimens directly 

 to proximus. 



I suggest, then, that the form now known as sauritus has had a 

 double origin, i. e., the coastal plain section from saclceni and the trans- 

 Allegheny section directly from proximus. This is what we might 

 expect, for the fact that the ribbon snakes are so eminently adapted 

 to the coastal plain conditions would favor the rapid invasion of the 

 eastern coastal plain from Florida, while the Appalachian system would 

 prove more of a barrier to such an aquatic form than to a more ter- 

 restrial one, and permit the section from beyond the Mississippi to 

 push into the region west of the Appalachians. However this may be, 



