i911] Bryant: Horned Lizards of California and Nevada 53 
that is found in every other species in a class (Diapsida) as far 
as is known. The intense heat of the desert fails to account for 
it, for Phrynosoma platyrhinos, a co-inhabitant of the same des- 
ert, and P. modestum, a near neighbor on the east, both show 
well-developed supratemporal openings. P. modestum, although 
a smaller lizard, presents by far the largest openings. The full 
development of the horns in Anota maccalli might call for a 
strengthening of the parietal and temporal region. The closure 
of the opening gives fully four millimeters more of suture in 
the adult, thus undoubtedly strengthening the horns to a consid- 
erable extent. The skull of A. maccalli is far more delicate in 
structure than that in any of the other species. Phrynosoma 
blainviller blainvillei develops horns just as long as those of 
maccalli, but their ratio to the width of the head is much less 
(see tables of measurements). Then, too, blainvillei has very 
heavy parietal bones, so that the need of strengthening the horns 
by means of a longer suture is not so apparent. It seems reason- 
able to believe, therefore, that in the evolution of this pecuhar 
form there has taken place a strengthening of the horns through 
a closure of the supratemporal openings by the fusion of the 
surrounding bony elements. 
Several other osteological characters, such as the well-devel- 
oped spines of the lower mandible and the dome-shaped parietal 
region, separate the type maccalli from other species of horned 
lizards, but are best not definitely regarded as purely generic 
characters. 
One of the most distinctive external characteristics is the 
flat tail. No other known species of horned lizards shows this 
peculiarity. As this flattening of the tail is accompanied by 
an associated osteological character, well-developed transverse 
processes on each of the caudal vertebrae, this character can well 
be considered diagnostic of this genus. Flat-tailed horned lizards 
as distinguished from other horned lizards would make a well 
defined group. 
