Cope. J °< jyj [April 5, 18T8. 



genus Pareiasainus 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 

 Pdycosauria, 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 Pelycosauria 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. The age 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 Palaeozoic. 

 In discussing the age of the Olepsydrops 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, Gtenodus and Diplodus, in both localities, renders this course 

 necessary. 



Theses. 



1. The horizon of the Olepsydrops 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 BatracMa. 



3. That in the land vertebrata of this period, the amphiplatyan, proccelous, 

 and opisthoccelous 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 Bhynchoceplialia 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 

 Bhachitomus and TrimerorliacMs, 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. 

 Published May 8, 1878. 



