Art. VI. ] Herrick-T^rry-Herrick, JVew Mexico Lz^ards, 133 
bb. Head spines moderately large, occipitals as long as 
the transverse diameter of the eye; gular scales 
perfectly smooth, . . P. orbiculare. 
aa. Several longitudinal series of enlarged pointed gular scales; 
a series of large spinose plates below the lower 
labials; head spines long, 
b. Gular scales spinose. 
c. Head shields convex and almost smooth. P. blainvillii. 
cc. Head shields flat, with numerous ridges and granula- 
tions, . .... P. frontale. 
bb. Gular scales feebly keeled. 
c. Occipital spines extend upward and outward. 
P. boucardii. 
A A. Nostrils opening in the line of the canthi rostrale or 
slightly above; several longitudinal series of en- 
larged gular scales; a series of very large bony 
shields below the lower labials. 
a. Occipital spines directed obliquely upward, like the tem- 
porals; ventral scales smooth, . P. coronatum. 
aa. Occipital spines vertical, erect; ventral scales keeled. 
P. asio. 
AAA. Nostrils pierced within the canthi rostrale ; gular scales 
small, equal or with one series of enlarged ones 
on either side. 
a. Tail longer than the head. 
b. Head bordered posteriorly by a series of contiguous 
large spines, of which four are occipital. P. regale. 
bb. Two occipital spines larger than the other head 
» spines, with an interval between their bases and 
those of the temporal. 
c. Enlarged dorsal tubercles spinose, erect; tympanum 
naked, .... P. cornutu 7 n. 
cc. Enlarged dorsal tubercles flat, or feebly raised; 
tympanum covered with scales; occipital spines 
as long as the horizontal diameter of the orbit; 
two or three series of peripheral spines; 18-20 
femoral pores, , , . P, platyrhynus. 
