The Skull of Labidosaurus. 7a 
tiles as an element distinct from the hypocentrum, would seem to dem- 
onstrate the fallacy of any arguments in favor of the exclusive origin 
of reptiles from the known microsaurs. The only legitimate conclu- 
sion one may reach is that we have generally erred in the assumption 
that reptiles arose in Permian times from known types of amphibians. 
I believe that we have yet to discover the ancestral amphibians, 
which were neither microsaurs nor temnospondyles in the present 
sense, at least as far back as early Pennsylvanian times, and I also 
believe that these ancestors had not only five toes in front, as have 
the Eryopidee, with at least the modern reptilian phalangeal formula, 
but that they also possessed cleithra, and rhachitomous vertebre. 
Of the Cotylosauria the form hitherto best known is, perhaps, 
Labidosaurus, a restoration of which has been published by Broili,? 
with a partial description of the grosser characters of the skull. The 
material of this genus in the collections of Chicago University, for 
the most part obtained by the expedition of 1908,* is probably the 
best yet secured. It consists of two excellent skulls, of typical size, 
three nearly complete skulls of smaller size, and portions of four 
of five others. Among these smaller skulls is the one described 
by myself as Pariotichus (Labidosaurus) incisivus Cope.? That 
the specific determination is wrong is very evident. Cope long ago 
figured the duplicate rows of maxillary teeth in his Pariotichus 
incisivus,’ whereas this specimen, like the typical labidosaurs, has 
but a single row, the essential character of the genus, a character 
indeed which induced Cope to separate the genus from the true 
Cotylosauria and refer it to the Pareiasauria. That Labidosaurus is 
closely related to Pariotichus is, I believe, assured, and its separation 
by more than family rank therefore improper. That all of these 
skulls belong in the same species as do the larger ones, L. hamatus, 
is improbable, but their specific determination at the present time is 
*Paleontographica, li, p. 65, 1904. 
‘Several additional skulls and skeletons were obtained by the expedition 
of 1909. 
*"Case, Zoological Bulletin, ii, p. 231, 1899; Williston, Journal of Geology, 
Xvi, 139, 1908. 
*Trans. Amer. Phil. Soc., 1886, p. 290, pl. ii, ff. 4, 5. 
