162 BULLETIN U4, UNITED STATES NATIONAL MUSEUM. 



From nelsoni it is chiefly distinguished by the entirely black snout, 

 and the completely black areas on the belly, between the white 

 rings, and the narrower red areas. 



Habitat and Jiahits. — Of these nothing is recorded. 



Range. — This form is best known from extreme southern Texas 

 and northeastern Mexico. One from Peubla, Mexico, is referable to 

 annulata, and one in the British Museum, labeled '^Tehuantepec, " 

 belongs probably to this form (Boulenger, 1894, 205). It should 

 be looked for in the plateau region of southern and eastern Mexico; 

 westward it apparently intergrades vfitli nelsoni. Since the gerdilis 

 of Arizona and New Mexico is most closely related to this form, the 

 latter may be expected to range pretty well north in Mexico, east 

 of the Sierra Madre. The only reliable record, aside from those 

 included in the list of specimens examined, is that for Tehuantepec 

 (Boulenger, 1894, 205). 



Variation and affinities. — This form has never been collected in 

 numbers, and the great majority of specimens obtained have come 

 from northeastern Mexico and extreme southern Texas. Future 

 collecting will undoubtedly extend its known range and increase the 

 limits of its variation. Specimens from Cameron County, Texas, 

 and the adjacent country in Mexico are typical and homogeneous; 

 they need not be confused wath the gentilis from farther north nor 

 with the Mexican forms of the triangulum group. The ventrals here 

 range from 197 to 210 — a number that is low for polyzona, a little 

 lower than neJsoni, and a little high for gentilis and amaura. A 

 specunen from San Antonio, which has been referred to gentilis, has 

 193 ventrals, and one from Puebla has 213. Boulenger's specimen 

 (1894, 205) from Tehuantepec, v/hich is probably close to annulata, 

 has 218 ventrals. This indicates that on the plateau region of 

 southern Mexico annulata may be characterized by a higher average 

 number of ventrals than it possesses in the northern part of its rarige. 

 The same may be true of the dorsal scale rows. The Puebla specimen 

 has the formula 23-21-19, while of those from the type region, only 

 3 out of 10 have the formula 23-21-19, the rest having it 21-19. This 

 is significant of the reduced scutellation that will be noticed to charac- 

 terize the forms of the triangulum group northeast and east from 

 here. 



The labials are, as usual, 7 and 9, but 10 in the low^er row is attained 

 by occasional specimens from^ the type region. The temporals are 

 usually 2 + 3 + 4, with infrequent drops of one in the second and 

 third rows. The posterior chin shields are a little shorter or about 

 equal to the anterior, and the loreal is oblong. The tail is about the 

 same length as that of poly zona, sl little longer than that of the major- 



