VARIATIONS OF GARTER-SNAKES. 125 



The E. macrostemma is the more ar-tive, sooner seeking the water, where it swims 

 keeping close to the shore, and remaining more or less in sight until it conceals itself 

 in a hole. The E. meianog aster, on the other hand, lies cjiiictly so as to be more easily 

 taken in the hand; but, if it once takes to the water, it seeks the depths and is no more 

 seen. It is much less disposed to bite than the E. macrostemma; the latter being, 

 like its ally, the E. sirtalis, a very pugnacious snake. 



A number of specimens have been taken about Lakes Xochimilco 

 and Chalco, Mexico. 



Range. — In contrast to angusHrosfris, which occurs on the northern 

 part of the ]\lexican })lateau, inelanogasUr lias thus far been recorded 

 only from that part of the plateau which lies south of the 26th par- 

 allel. From this latitude it extends southward to Puebla, but has 

 not been recorded from that State. Over the northern part of this 

 region the environmental conditions are the same as in the northern 

 part of the plateau, but to the southward the precipitation increases 

 with the result that permanent rivers and lakes are formed. 



Specimens have been examined from the following localities: 

 Coyotes and Durango, Durango; Ocatlan, Jalisco; Lakes Xochimilco 

 and Chalco, and ^lexico City, Mexico; l)esides a number of others 

 with no other locality label than "Mexico." Giinther (1894, 134) 

 records the following general localities: Guanajuato, Veracruz, 

 Tehauntepec. Owing to its relationship to angusfirostns, we do not 

 believe that it occurs north of Coyotes, Durango, but the locality 

 records probablv do not represent the southern liudt of its range 

 (fig. 53)._ 



Variation. — As in the case of angustirostris , far too few specimens 

 of this snake are available to reveal whether or not geograjihic vari- 

 ation in scutellation exists. Certain general facts should ])o pointed 

 out, however. The dorsal scale formula is 19-17 in every specimen 

 examined, the ventral plates vary in number from 139-158 (average 

 145-150), the subcaudals from 49-67 (average about 58). These 

 numbers indicate ])lainly that melanogaster has a distinctly reduced 

 scutellation from the maximum for the genus, a fact which is not 

 disproved by the lal)ial formida. Thus, the supralabials are nearly 

 always 8, the only differences consisting of a loss of a single plate, 

 while the normal number of infralabials (10) becomes occasionally 

 9, and in but one instance 11. The tail length, as previously stated, 

 A^aries from .19 (female) to .26 (male), the average length for every 

 locality with two or more specimens being .22. 



Affinities. — I have already pointed out in the discussion of the 

 affinities of arigustirostris: that these two forms are evidently related 

 in that the strongest distinguishing characters possessed hy angus- 

 tirostris (the segregation of the eye from all but one labial and the 

 ])resence of more than two preocidars) a]i])arent]y disappear in that 

 part of the range which it shares with ritelanogaster. It is natural 



