VARIATIONS OF GAETER-SNAKES. 125 



The E. macrostemma is the more active, 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. vielanogaster , on the other hand, lies quietly 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. macrosterruna; 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 angustirostris, which occurs on the northern 

 part of the Mexican plateau, melanogaster has 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 Alexico City, Mexico; besides 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 angustirostris, we do not 

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

 records probably do not represent the southern limit 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 geographic vari- 

 ation in scutellation exists. Certain general facts should be 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 plainly that melanogaster has a distinctly reduced 

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

 disproved by the labial formula. 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, 

 varies 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 angustirostris that these two forms are evidently related 

 in that the strongest distinguisliing characters possessed by angus- 

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

 presence of more than two preoculars) apparently disappear in that 

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



