172 



MISS JOAN B. PROCTER ON THE 



often each show a delicate arrangement of black pigment standing 

 out from the ground-colour and having the same pattern effect 

 as the fine dendritic marks seen in many rocks. This arrange- 

 ment is often exactly repeated from one scale to another. When 

 this style of markings is present on the clear yellow of the 

 ventral shields, it produces a dark green effect, merging, when 

 seen at a distance, into the ground-colour. 



IV. Individual Variation and Evolution of Markings. 



Individual Variation. 



As a starting-point in the study of the markings and colour 

 varieties of L. atrox, it was .suggested to me by Mi'. Boulenger 

 that I should make an examination of a female and her 26 young 

 from Trinidad (received from Mr. Urich) in order to ascertain 

 the amount of individual variation among specimens unquestion- 

 ably pertaining to one form only. 



The young snakes range from 160 to 300 mm. in length, and 

 are more brightly marked than their mother. Their ground- 

 colour is a soft shade of brown, except the tip of the tail, which 

 is a pale yellowish. Particulars as to the number of ventrals 

 and subcaudals etc. will be found in the annexed table. In the 

 majority of cases, the pattern on each side is made up in the 

 following way, as shown on text-fig. 3 : — 



Group A consists of the six primitive spots arranged in a 

 pyramid (see text-fig. 2, p. 171). A large triangular or rather 

 trapezoid spot (A 1, dorsal series) forms the apex, and rests 

 upon two small rhombic spots (A 5, 6, dorso-lateral series), which 

 are sometimes confluent with it. These rest upon three similar 

 spots, the outer ones being somewhat the larger (A 2, 4, 3, lateral 

 series). This triangular marking is margined in cream-colour, 

 and encloses an area darker than the surrounding ground-colour, 

 a state of things which seems to suggest a centripetal aggregation 

 of pigment. Group A, though equal in size to group B, is in 

 every case darker and more marked. 



Group B is also triangular in form, but the base coincides with 

 the mid-dorsal line, instead of the apex as in group A. The said 

 base is composed of three oval spots (B 5, 1, 6, dorsal series), the 

 middle one being much the largest. Three more small oval spots 

 enter the remainder of this triangle, the largest at the apex 

 „ (B 3, 4, dorso-lateral, B 2, lateral). (Text-fig. 3, A.) 



When the markings of the two sides of the snake correspond 

 exactly, the general dorsal design is a single string of light- 

 spotted ovals on a dark ground ; this is formed by the paired 

 groups B having their bases applied together. They appear oval 

 rather than diamond-shape, on account of the curved border of 

 the ground-colour of these groups. If the markings should alter- 

 nate with each other, a light wavy band on a dark ground is the 

 general result. Usually, however, a single specimen exhibits 



