VARIATIONS OB^ GARTER-SNAKES. 45 



is unfortunate, as a knowledge of its habitat would undoubtedly 

 throw much light upon the explanation of its distribution. At first 

 sight it seems rather surprising that a species of this genus should 

 occur so abundantly in an arid region, and three alternative explana- 

 tions present themselves. It may be either a distinctive desert type 

 and confined to arid localities even in the more humid (southern) 

 portions of its range, or it may, on the other hand, be addicted to a 

 more aquatic habitat, being confined in the desert regions to the 

 vicinity of water. As a third alternative it may be that the form is 

 able to adjust itself to either arid or moist conditions, a change that 

 if extensive might necessitate a change of habits. 



The second explanation is probably most nearly the true one, for 

 the genus is notably inclined toward a moist habitat. Cope in 1885 

 (1885a, 386-387), writing of the habits of this snake at Lake Xochi- 

 milco, near the City of Mexico, says, ''The ends and shores of the piers 

 are the resting places of innumerable water snakes, which can readily 

 be observed from a canoe. * * * We caught a considerable number 

 and found that they belong to the two species above named [insignia- 

 rum and melanogaster]. The E. insigniarum is the most active, 

 sooner seeking the w^ater, where it swims, keeping close to the shore, 

 and remaining more or less in sight until it conceals itself in a hole. 

 * * * The food of both of these species is the Rana montezuma 

 Baird and another species allied to Rana halccina." 



Again (1900, 1030) he writes: "On being disturbed the E. macro- 

 stemma plunges 4nto the water, but does not go far beneath the sur- 

 face, but takes refuge under the edge of a bank, or emerges in a new 

 spot, so that it is difficult of capture. The columns that support the 

 aqueduct that carries water from Chapultepec to the City of Mexico 

 are covered with a dense vegetation, which is continuously watered 

 by leaks in the venerable structure. On examining this vegetation 

 at my height above the ground, I encountered in the thick "of it a 

 round eye. Exposure revealed first the head and then the body of 

 a snake of this species, which found a congenial abode there." 



Baker in 1895 (1895, 120-121), in speaking of a trip on Lake Patz- 

 cuaro says, "As we approached the island, a commotion was ob- 

 served in the water, and a snake was seen to glide swiftly and noise- 

 lessly away. I quickly shot it; on picking it up we found it to be a 

 large species of water snake ( E. insigniarum) . As we pushed our 

 boat among the reeds bordering the island a great commotion w^as 

 created in the water and a number of these snakes were seen to swim 

 away." 



From these accounts and the large numbers of specimens in difi'erent 

 museums from the lakes of southern Mexico, there can be no doubt 

 that megalofs in southern Mexico not onl}" thrives in a moist locality 

 but is also quite ac^uatic in its habits. In contrast with these descrip- 



