MEXICAN HERPETOLOGICAL MISCELLANY—SMITH 381 
The southern Chiapas specimens are characterized chiefly by their 
dull color, which differentiates that population from all other marga- 
ritiferus of Central America, Mexico, and the United States. To this 
the name occidentalis Bocourt is applicable. In mature specimens of 
this race the hight central spot of each dorsal scale (characteristic of 
the whole species) is gray-brown, diffuse, poorly defined, and stippled 
with darker. Young specimens are the same, except that the light 
areas are better defined. In all other mature specimens of the species, 
from Costa Rica to Texas, the ight central spot is blue, or yellow to 
orange, or is partly blue and partly yellow or orange. The difference 
is striking, even in many long-preserved specimens (unless badly 
discolored by formalin). 
Correlated with this color difference in occidentalis are two readily 
discernible differences in pattern. The most uniform difference, but 
perhaps less readily defined in words and also perhaps varying with 
age, is the complete absence (in mature specimens) or poor definition 
(in young specimens) of the dark area on the side of the head. 
Of all other specimens of the species this dark area is very charac- 
teristic, is well defined, and (as a key basis of comparison) is much 
darker than the general tone of the median dorsal nape area (equal 
in occidentalis). A more easily definable pattern difference of occi- 
dentalis is the complete absence of black edges on the subcaudals; 
the ventral surface of the tail is white, totally immaculate. Many 
specimens from the Atlantic slopes of Mexico and Texas have been 
checked for this character, and without a single exception all have 
the posterior edges of the subcaudals black. Frequently the belly 
scales are black-edged also (not or only laterally in occidentalis). 
This character, therefore, completely separates Atlantic coast Mexi- 
can and United States margaritiferus from occidentalis, but the char- 
acter fails when applied to Pacific coast specimens from Tehuantepec 
north, in which is found the proportion of one white-tailed specimen 
to two banded-tailed specimens, with some specimens arbitrarily allo- 
cated to one category or the other. 
Accordingly, other differences were sought, and it was then dis- 
covered that Pacific coast specimens uniformly differ from Atlantic 
coast specimens in having black the entire border, anterior as well as 
posterior, of the middorsal scales (not the extreme lateral scales). 
In Atlantic coast specimens the posterior border of the middorsal 
scales is black, but the anterior borders (from center) are blue; in 
discolored and young specimens, of course, the anterior borders do 
not appear blue, but are readily discernible as lighter and well dif- 
ferentiated from the jet black border of the posterior edge. The 
difference is not uniformly discernible in the pattern of the lateral 
scales, but is well defined on the middorsal scales. 
469013—42——3 
