COLORATION 33 



such as the annulate form in the South American 

 Elaps, this is far from being universally the case ; 

 many closely allied species, or individuals of the 

 same species, may be distinguished by very different 

 patterns. Even on the same individual we may find 

 two opposite types of markings without any transi- 

 tion, as in two Central American species of widely 

 different genera, Polyodontophis annulatns and Zamenis 

 mexicanus, in which the anterior part of the body is 

 annulate or barred, and the rest longitudinally 

 striped. 



It is also a remarkable fact that very often the 

 two sides of the body are not alike in their markings, 

 appearing as if formed of the union, on the median 

 line, of the right and left halves of two individuals. 

 Thus it may happen, in annulate forms, that some of 

 the annuli are broken exactly in the mid-dorsal and 

 mid-ventral lines, and that the halves do not corre- 

 spond in number on the two sides. In the hand- 

 some South American Lachesis altematus, which 

 derives its specific name from the two series of 

 large C-shaped, dark, light-edged markings which 

 adorn its back, these markings are not always alter- 

 nating, as is the rule ; but some may lie opposite 

 to each other and back to back, this being due to 

 the fact that the numbers of the markings do not 

 correspond on the two sides. In one specimen I 

 count twenty-four of these markings on the left side, 

 and twenty-seven on the right. This shows tnat 

 3 



