Cope. ] 530 [April 5, 1878- 
genus Pareiasaurus Ow., he gives a special name, expressive of the deeply 
impressed surfaces of the centra occupied by the remains of the chorda 
dorsalis. As this, or the perforate condition, is characteristic of all of the 
Pelycosauria, it is probable that it is present in Prof. Owen’s Therodontia 
also. It is also evident that since the dental characters of Pareiasaurus 
do not serve to distinguish it as an order from the genera with distinct 
canine teeth, this group also must be looked upon as a subdivision, per- 
haps of family value, of the Pelycosauriaw or other parts of the Rhyncho- 
cephalous order. 
The Texan genera of this group, so far as yet known, are about equally 
related to the Ural and South African types. Theage of the former deposit 
is the Permian, which includes, according to Murchison, the Todtliegende 
and Zechstein of Thuringia. The age of the South African beds is uncertain, 
but is suspected by some authors to be Triassic, and by Owen to be Paleozoic. 
In discussing the age of the Clepsydrops shales of Illinois, which had been re- 
ferred to the coal measures by all previous investigators, I left the question 
open as to whether they should be referred to the Permian or Triassic 
formations.* The evidence now adduced is sufficient to assign the forma- 
tion, as represented in Illinois and Texas, to the Permian. Besides the 
saurian genera above mentioned, the existence of the ichthyic genera 
Janasso, Ctenodus and Diplodus, in both localities, renders this course 
necessary. 
THESES. 
1. The horizon of the Clepsydrops shales of Illinois and correspond- 
ing beds in Texas is Permian. 
2. That this period witnessed an abundant life of land and ichthyic ver- 
tebrata, the former consisting of Rhynchocephalian reptiles and Stego- 
cephalous Batrachia. 
3. That in the land vertebrata of this period, the amphiplatyan, proccelous, 
and opisthocelous types of vertebral articulation were unknown, and that 
the vertebral centra are either deeply amphiccelous or notochordal. 
4, That in the case of both the Rhynchocephalia and Stegocephali, a spe- 
cialized dentition, and in the former order, a specialized limb structure, were 
superadded to this imperfect vertebral structure. 
5. That in the primitive land Vertebrata of the Permian, the place of the 
vertebral centrum was occupied by two elements, the centrum and inter- 
centrum. 
6. That the intercentrum, from a position of primary importance, as in 
Rhachitomus and Trimerorhachis, became reduced, and finally mostly ob- 
literated, but that it remains at the present day in the anterior dorsal re- 
gion of some Lacertilia, and as the chevron bones of most reptiles and 
some mammals. 
* Proceedings Academy Philadelphia, 1875, p. 405, 
