SYNOPSES AND DESCRIPTIONS "5 
others by an interspace. Head, neck, and body very distensible. Tail 
short, pointed. Seales keeled or smooth. Subcaudals bifid. United 
States to the Argentine Republic. 
Azygos shield in contact with the prefrontals platyrhinus. 
Azygos surrounded by small plates simus. 
HETERODON PLATYRHINUS, pl. VI., fig. 5. 
Latreille, 1802, Hist. Nat. Rept. IV, 32, pl. XXVIII, fig. 1-3. 
Stout, tapering backward, body, neck and head very distensible; head 
broad, short, slightly convex on the crown; tail short, near one sixth of 
the total, tapering. Eye large, surrounded on sides and below by small 
scales, pupil round. Mouth-cleft moderate, forming a single curve with 
the anterior face of the rostral. Posterior maxillary teeth larger, smooth, 
separated by an interspace from the others. Crown-shields broad. Su- 
praciliaries large. An azygos shield behind the rostral, in contact with 
the internasals. Internasals subtriangular, separated by the rostral and 
azygos. Rostral very prominent, curving upward into an acute-edged 
e internasals. Nasal in 
Ocu- 
lars ten (9—14). Temporals varying, three to four. Labials eight, sixth 
trihedral or shovel, with a sharp ridge be 
two parts, the valvular nostril between. Loreals two, lower larg 
and seventh large. Infralabials eleven, third and fourth large. Sub- 
mentals one pair, followed by small shields, in contact with three labials. 
Seales keeled, broad at the extremity, in twenty-five rows (23—25), dorsal 
narrow, caudal and outer row broad, first row smooth. Ventrals 120—150. 
Anal bifid. Subcaudals 45 
Reddish or yellowish-brown to black (var. niger). A series of twenty to 
60 pairs. 
thirty dorsal spots, usually surrounded by a margin of very light color. 
Tail with about nine transverse bands. On the upper portion of the flank 
there is a series of medium-sized spots alternating with the dorsal; below 
this there are three or four alternating series of small more or less indistinet 
spots, the lower encroaching upon the ventral scales. Yellow under the 
chin and throat, darkening posteriorly and becoming olivaceous mottled or 
blotched with brown. <A dark light-edged band across the prefrontals 
through the eye to the angle of the mouth. A similar band on the frontal 
and supraciliaries just behind the eye, more or less joined with the broad 
band from each parietal to the sides of the neck. Immediately behind the 
