6 BULLETIN 114, U]SriTED STATES l^TATIONAL MUSEUM. 



trals, which vary in number, in the genus, from 152 to 254. These 

 are terminated posteriorly by a single anal plate (found divided in 

 only three specimens examined, one triangulum, one elapsoides, and 

 one calif orniae, and it is reported as divided in the type of CoroneUa 

 formosa anomala Bocourt). The plates under the tail, or caudals, 

 are normally in two rows, but occasional individuals have one or 

 several of these entire (particularly in micropJiolis, pyrrhomelaena, 

 and some forms of getulus) ; they vary in number in the genus from 27 

 to 79. 



The head is but slightly distinct from the neck, except in a few 

 specialized or aberrant forms in which it is plainly wider at the 

 temples (pyrrhomelaena, alterna, mexicana, and micropholis) . The 

 body is in general slender, of nearly uniform diameter, cylindrical 

 above, the sides meeting the belly in a noticeable angle. The tail 

 is short, tapering rapidly to a horny tip, and varying from 0.09 to 

 0.18 of the total length; only a few aberrant forms have it commonly 

 longer than 15 per cent of the total length (mexicana, alterna, and 

 pyrrhomelaena). The sex of an individual may in a majority of 

 cases be told by the shape of the posterior end of the body. When 

 the body is viewed from the side, an abrupt slope on the dorsal 

 line from body to tail indicates a female, a gentle slope a male. 

 Viewed from below, the tail of a female is .much narrower at the base 

 than that of the male. The tail of the male must be larger at the 

 base in order to contain the copulatory organs, while the body of 

 the female must be larger near the end to hold the eggs; therefore the 

 sudden change in diameter in the female where the body meets the 

 tail, and the gradual change in the male. 



No fundamental pattern of coloration holds throughout the genus, 

 but, except for two isolated forms of dubious aflSnities (mexicana and 

 alterna), all the styles of coloration may be put into three groups. 

 In one (the getulus group) the pattern is fundamentally an oval 

 white center in a black scale, and from this may be derived every 

 other arrangement in the group, including two other kinds of spotted 

 patterns, two of cross bands, one of rings, and one of longitudinal 

 stripes. In another (the calligaster group) the pattern is of numerous 

 black-edged brown blotches set on a ground color of lighter brown. 

 In the third (the triangulum group) the pattern is of encircling rings 

 of white or yellow, bordered with black, and separated by red. By a 

 joining on the ventral plates of the black borders of adjacent pairs 

 of black rings the red becomes restricted to dorsal saddles, and by a 

 migration upward, onto the dorsal scales, of these black borders the 

 red finally becomes restricted to dorsal blotches, and in this case, 

 smaller blotches are developed on the sides in alternation with those 

 above. In this group red is a fundamental and almost universal 

 color, but when it becomes restricted to dorsal blotches it changes to 



