4 University of California Publications in Zoology (Vou. 9 
Harlan (1825) was the first one to class the horned lizards 
in the genus Agama, his reason for so doing being the presence 
of femoral pores. He described the Texas horned lizard under 
the name Agama cornuta, calling attention to the fact that “‘It 
approaches nearest the Agama orbicularis Daudin (1802) or the 
Lacerta orbicularis Linnaeus (1787), the Tapayaxin of Seba, 
who has given three figures of the species.’’ Four years later, 
Harlan (1829), in a synopsis of the reptiles of North America, 
describes but one species, Agama cornuta and gives its distribu- 
tion as ‘‘transmissippi territories as far west as the plains of 
the Columbia River, and as far south as Arkansa [sic/].”’ 
The Oregon horned lizard, Phrynosoma douglassi, was also 
placed in the genus Agama by Bell (1828). In the same year 
Wiegmann (1828) placed all of the known horned lizards in a 
new genus by themselves which he termed Phrynosoma. Girard 
(1858) divided this genus into four subgenera, Tapaya, Batra- 
chosoma, Phrynosoma, and Doliosaurus. The subgenerie char- 
acters not being diagnostic, but few have used this classifica- 
tion. Cope (1898), instead of following the classification of 
Girard, divided the genus into two genera, Phrynosoma and 
Anota, basing the division on the character of the auricular 
aperture. This would seem to be the best division that could be 
made were it not for the numerous instances of intergradation 
to be found. Both Phrynosoma platyrhinos and P. modestum, 
two species grouped under the genus Anota in which the 
tympanum is concealed by a scaly integument, show wide 
variation in this respect, all gradations from an almost naked 
tympanum to one entirely concealed being found within each 
species. 
One grouping used by Cope (1898) and Van Denburgh (1897) 
based on the position of the nostrils, divides the species into well 
defined groups, but those within each group are so unlike in 
other characteristics and in distribution that even this division 
is unsatisfactory. 
The bases for generic and specific distinction among the 
horned lizards have not as yet been generally accepted owing 
to this difficulty experienced in finding dependable characters. 
