SYNOPSES AND DESCRIPTIONS 75 



others by an interspace. Head, neck, and body very distensible. Tail 

 short, pointed. Scales 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, pi. VI., fig. 5. 



Lalreille, 1802, Hist. Nat. Kept., IV, 32, pi. 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 

 trihedral or shovel, with a sharp ridge between the internasals. Nasal in 

 two parts, the valvular nostril between. Loreals two, lower larger. Ocu- 

 lars ten (9 — 14). Temporals varying, three to four. Labials eight, sixth 

 and seventh large. Infralabials eleven, third and fourth large. Sub- 

 mentals one pair, followed by small shields, in contact with three labials. 

 Scales 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 — 60 pairs. 



Reddish or yellowish-brown to black (var. niger). A series of twenty to 

 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 indistinct 

 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 



