22 University of California Publications in Zoology (Vou. 9 
scales. In the former, even a depression is scarcely discernible. 
The latter, however, shows clearly the location of the opening. 
That this unusual modification is some particular adaptation 
to environment would seem to be proved by its prevalence among 
all truly desert species of horned lizards. None of the other 
iguanids except Holbrookia show this adaptation, however. <A 
slight reduction in size in P. platyrhinos and a greater reduction 
for A. maccalli is also to be noted in this connection. 
KEY TO GENERA AND SPECIES 
[Based in part on that of Van Denburgh (1907) | 
A. Horns flattened and grooved; one or two rows of peripheral spines; tail 
rounded; supratemporal openings present .... Phrynosoma 
a. Nostrils on the line joining the supercillary ridge with the end of the 
snout, 
b. One row of peripheral spines; occipital horns rudimentary; no 
TOWwseOh enlarcedeoulantscalles yess eee P, douglassi 
ec. Size small (70-90 mm.); horns mere tubereles; snout blunt; 
coloration inconspicuous .......-..---..-.----------- P. douglassi douglassi 
bb. Two rows of peripheral spines; occipital horns well developed; 
three rows of enlarged gular scales ...............-.-...--- P. blainvillei 
d. Head shields conyex and almost smooth, centrally located ones 
largest P. blainvillei blainvillei 
dd. Head shields flat, with numerous ridges and granulations, size 
MUL ORMIY SMa kee oe ar P. blainvillei frontale 
aa. Nostrils above the line joining the superciliary ridge with the end 
of the snout. 
e. Horns short (4-8 mm.); one row of peripheral spines; six to 
twelve: femoral pores) ca.<Joce-ccedeesetens tae acces een pence ona eee P. platyrhinos 
AA. Horns long (8-12 mm.), smooth and conical; three rows of closely-set, 
peripheral spines; tail flat; supratemporal openings absent ......Anota 
/. Nostrils anterior; sixteen to twenty femoral pores —............/ A. macealli 
Phrynosoma douglassi douglassi (Bell) Stejneger 
Pigmy Horned Lizard 
Agama Douglassi Bell (1828), pp. 105-107, 1 pl. 
Phrynosoma douglassi Girard (1853), pp. 861-362, pl. 7, figs. 6-10. 
Tapaya douglassi Girard (1858), pp. 397-399, pl. 21, figs. 1-5. 
Phrynosoma douglassi pygmaea Yarrow (1882), p. 443. 
