VARIATIONS OF GARTER-SNAKES. 55 



suggested, the tendency , if it exists, is not at all well defined. As 

 regards the number of subcaudals and tail length in Arizona, the luini- 

 ber of available specimens is far too small to settle this point, although 

 the maximum number of subcaudal plates in the males is 86, while 

 the tail length remains the same as in the Chihuahuan specimens. 

 As regards the number of ventral scutes there is an apparent reduc- 

 tion, since the maximum number, even in the males, is but 165, while 

 the minimum exhibited by the females is 153. It is to be observed, 

 however, that although chiefly male records of the number of urosteges 

 are to be had, this is due to the fact that it is the tails of the females 

 in this lot that are mostly injured, and that the females actually 

 predominate in the records, which explains the low number of ven- 

 trals. In respect to the labials the average at Tucson is 8.3, wdiich 

 is practicall}^ the same as m Chihuahua. The similarity in scutel- 

 lation and tail length between Arizona and Chihuahua specimens is 

 thus very close, and there is no reason to believe that a larger number 

 of specimens will materially disturb it, so that it is impossible to 

 divide the group here on this basis. 



One more trait of the Mexican megalops remains for us to examine. 

 Nearly the same difficulties have arisen over the attempt to dis- 

 tinguish different forms within this species on the basis of color as we 

 have seen above to have arisen in the attempt to divide it on the 

 basis of tail length. As is well established by the specimens, there is 

 a consitlerable range of variation in color, but it remains to be seen 

 whether this is individual, sexual, or geographic. In general the 

 color may be defined as some shade of olive or brown, wuth three 

 light stripes distinct or obscure. The lateral is on the third and 

 fourth rows, anteriorly, posteriorly on the third only, on the second and 

 third, or indistinct. The dorsal stripe covers a varying distance of 

 from 1 to 3 scale rows on either side of the median dorsal one. The 

 lateral spots are obscured on the scales in the dark specimens, but 

 are distinct in the lighter ones, and when present occur on all but 

 the keels of the involved scales. Of the variations of this general 

 type four color phases may be noted: 



First. The ground color is dull brownish olive, with the lateral 

 spots visible on the edges of the involved scales, but not prominent, 

 owing to the dark color. The lateral stripe is greenish olive, the 

 dorsal stripe dull greenish yellow on the median and one-half of the 

 adjacent rows, the edges not being well defined. The supralabials 

 are dark greenish yellow, narrowl}' margined with black; the head 

 olive brown and the parietal spots very small. The belly is bluish 

 green, clouded with yellow anteriorly; the chin and throat also being 

 yellow. (1279, Field Museum.) 



Second. The ground color of the al)ove type may become so dark 

 as to appear nearly black, entirely obscuring the spots on the scales. 



