816 REPORT OF NATIONAL MUSEUM, 1898. 



toward tbe head, exhibiting a tendency to arrangement in two rows. 

 Extreme bases of all the scales black. 



The above expresses the condition of specimens of medium age. In 

 young examples the head i)lates have pale margins, and this character 

 sometimes persists in specimens of considerable size. The dark stripes 

 on the extremities of the gastrosteges is absent in half the specimens. 

 The lines on the middles of the dorsal scales are sonietimes wanting, so 

 that the back is uniform brown. Sometimes the space between the first 

 and third rows of scales is darker than that between the latter and the 

 middle of the fifth row, thus imitating the 31. laterale, but with the light 

 stripe thus outlined one row of scales higher up. 



The lateral jilates from the postoculars forward are yellow with 

 brown borders; the temporals are brown with yellow borders, thus dif- 

 fering from the M. schottiiy where they are unicolor. The superior 

 labials bave their superior and inferior edges brown bordered or rather 

 blotched, except the eighth, which has the lower edge yellow. Inferior 

 labials and genials marked with black specks or blotches. 



A young specimen (Cat. No. 81123) has the tendency to a yellow stripe 

 on the third, fourth, and fifth rows of scales above referred to, well 

 marked. The head shields above have narrow pale margins. The 

 frontal plate is not so narrow posteriorly as in the adult from the same 

 and other localities. Still younger individuals (Cat. Nos. 1982, 11423) 

 have the lateral yellow stripe more distinct by the suflusion of the third, 

 second, and half the first rows with brown, thus producing an appear- 

 ance much like that of the Z. lateralis. But only the third and fourth 

 rows have the yellow stripe, and the brown band covers the ends of the 

 gastrosteges of that species. It was this resemblauce that induced me 

 to combine the two species, with the remark ^ ''the young, of the form 

 laieralis, the adult, the twriiatus.^^ 



Measurements. — The measurements of the tail in nine sj)ecimens are 

 as follows: Three and one-seventh times in total length, Cat. Nos. 8432 

 and 4384; three and one- fifth, Cat. Nos. 9520, 8120, and 11422; three 

 and one-fourth. Cat. Nos. 13G18 and 1979; three and one-third, Cat. Nos. 

 8122; three and one half, Cat. No. 1983. 



The distribution of this elegant snake is throughout the Sonoran 

 region north to Salt Lake and western Colorado, and in the Pacific 

 north to Baird, Shasta County. I have met with it in the Eio Grande 

 Valley as far south as Laredo, Texas. I observed a specimen strung 

 through the branches of a screw-bean thicket. It eyed me for a time, 

 l>erfectly protected by the bard spines of the bushes, which prevented 

 me from seizing it. On being stirred up it moved off rapidly and grace- 

 fully through the branches. 



' Proc. Acad. Nat. Sci. Phila., 1866, p. 305. 



