1884.] Batrachia of the Permian Period of North America. 27 
characters were given as follows. I have not been able to expose 
the occipital condyle in my specimens. 
Centra and intercentra subequally developed as vertebral bodies, 
a single neural arch supported by one of each, forming a double 
body. Chevron bones supported only by intercentra. Basiocci- 
pital vertebral articulation connected with the first vertebra by 
an undivided discoid intercentrum. 
Thus the peculiarity of the vertebral column in general is car- 
ried into the cephalic articulation, and we have, instead of the 
complex atlas of the Rachitomi, a single body connecting the 
occipital condyle and first vertebra. This body represents, in all 
probability, zhe single occipital condyle of the reptilian skull. 
This part, as is well known, remains cartilaginous in the lizard 
long after the basioccipital is ossified,’ and is a distinct element. 
In the Urodele Batrachia it appears, according to Albrecht, as 
the odontoid process of the aé/as. The structure of Cricotus 
shows that it is a connate intercentrum. We have thus removed 
the last difficulty in the way of the proposition that the Reptilia 
are derivative of the Batrachia, viz., the difference in the cranio- 
vertebral articulation. But the former have not been derived 
from the Labyrinthodontia, as has been suggested, nor from 
the Rachitomi, but from the Embolomeri. The order of Rep- 
tilia which stands next to it is, of course, the Pelycosauria of 
the same period, which presents so many Batrachian characters, 
including intercentra, as I have for the first time pointed out 
in the paper above quoted. 
Professor Gaudry has been inclined to regard the bones which 
I have called intercentra as the true centra. But in the Embo- 
lomeri we have evidence that the pleurocentra are the true centra, 
since they assume the larger bulk, and support the neural arch 
and costal articulation, the intercentrum becoming more and 
more subordinate as we advance from the caudal series forwards. 
Moreover, the intercentrum bears the chevron bones in the 
Rhachitomi, and the Embolomeri, as they do in the cotemporary 
Pelycosauria. 
I add to the ordinal characters above given, that the three pec- 
oral shields of the Stegocephali are present here also. 
1See Parker On the development of the skull of the Lizard, Philosophical Trans- 
actions, London, 1879. ‘ 
? Intercentra remain in the cervical and dorsal series of Hatteria, and there is ro 
at least in the cervicals of the Pythonomorpha. 
