54 BULLETIN 61, UNITED STATES NATIONAL MUSEUM. 



proportionate tail length of .25, giving it the nanie of megalops. 

 Immediately following tliis he described a specimen from the City 

 of Mexico, by Major Rich, giving no measurements, prot)ably owing 

 to the fact that the tail was broken. In 1885 Professor Cope (1885b, 

 173), in giving a synopsis of these forms, listed as megalops a speci- 

 men collected by himself on Duck Creek, New Mexico, which had a 

 tail length of .26, and stated that TnacrosteTnnia (insigniarum) may 

 be distinguished by its shorter tail. In 1886 Cope (1886, 285) again 

 listed as megalops ten specimens collected by Wilkinson at Chihuahua 

 and stated that they did not differ from the Duck Creek specimen. 

 In 1892 (1892, 646), in a key to the species of garter-snakes, he gives 

 as the distinguishing differences that megalops has a tail length of 

 less than one-tliird and more than one-fourth the total length, while 

 in macrostemma it is more than one-fourth and not less than one- 

 fifth, and on a subsequent page (651) lists three specimens of macro- 

 stemma (insigniarum) said to be from near Prescott, Arizona, thus 

 extending the range of the latter to cover most of the region occupied 

 by the former. 



In 1901 Brown (1901, 22), in endeavoring to straighten out the 

 American representatives of the group, found in five specimens from 

 Mexico " the tail to be about one-fourth of the length, or longer than in 

 most adult megalops, which reverses the proportions given by Cope." 

 This threw the Arizona (insigniarum) specimens of Cope, which -as 

 Brown shows are from Tucson instead of Prescott, with megalops, 

 which now becomes distinguished from macrostemma by the presence 

 of a shorter tail; macrostemma is excluded from the United States, 

 being replaced by megalops in southern New Mexico and Arizona. 



The solution of this tangle is not hard to find if we take into con- 

 sideration the sex of the specimens. In the first place, both Ken- 

 nicott's type of megalops and Cope's Duck Creek specimens are 

 males, the latter having a slightly longer tail than is usual, while the 

 type of macrostemma (although not measured), and a number of 

 other specimens from southern Mexico examined by Cope were 

 females, while at least some of those that he measured (type of 

 insigniarum) from the latter region, although males, have short tails, 

 owing to the shortening that we have shown to take place toward 

 the southern part of the range. Finally, Brown's Tucson specimens 

 were females with characteristically short tails, which led him to 

 reverse Cope's description. 



As a matter of fact there is, as shown by our diagrams, a slight 

 decrease in the tail length of the tail to the southward. But the 

 amount is entirely too small upon which to distinguish a variety, 

 much less a species, and the same thing holds true m regard to the 

 scutellation. I have also stated that while a decrease in the 

 scutellation in the southern parts of New Mexico and Arizona is 



