52 University of California Publications in Zoology |Vou.9 
not show such wide differences in structure. In recognition 
of the distinct characters of maccalli the genus Anota is here 
emended to include this species only, the other species classed 
by Cope under this genus, being referred to Phrynosoma because 
of their intimate relations to the species of that genus. 
The genus Phrynosoma is so absolutely distinct from the 
other iguanids and in turn from all of the Lacertilia that any 
species with the horns, the enlarged tubercular scales of the 
back, and the peculiarly shaped head characteristic of the horned 
lizards, is naturally referred to this genus. It is interesting, 
therefore, that within such a specialized group one species alone 
should show such divergent specialization as to call for a sep- 
arate genus. The closure of the supratemporal openings alone 
seems to justify generic rather than subgeneric separation from 
the other horned lizards, for this character is without parallel 
among the Lacertilia. Osborn (1903) considered the presence 
of the supratemporal fenestra so constant that he used it as a 
character in dividing Reptilia into the subclasses, Synapsida 
and Diapsida. He says: ‘“‘The contrast between the elongate 
cranium and large supratemporal fenestra and the abbreviate 
cranium and short supratemporal fenestra is one of the striking 
differences between the Synapsida and Diapsida.’’ Although 
he does not discuss the presence of the opening in Lacertilia, 
its presence is inferred to be constant in that the Lacertilia are 
grouped under Diapsida. 
A thorough examination of all of the horned lizards of the 
United States showed the presence of the opening. Several of 
the rarer Mexican species have not been available, but these show 
close resemblance to other species which possess the supratem- 
poral opening. 
An examination of young specimens showed a very small 
opening, about the size of a pinpoint, to be present, which 
would lead one to believe that the opening is closed during the 
period of growth. In adult specimens the opening is entirely 
roofed over with bone, a suture being left between the parietal 
and supratemporal elements. 
It seems difficult to account for the closure of an opening 
