638 S. W. WILLISTON 



the genera mentioned above and the numerous ones known 

 from the American Permio-carboniferous. Two other, disputed 

 groups of contemporaiy air-breathers, beUeved to be reptiles 

 b}'' some authors of repute, will be discussed in the sequel. 



All of the so-called orders represented by these reptiles are 

 believed to be continuous, not only throughout the Permian 

 of Europe or Africa, but also throughout more or less of the trias 

 if not the mesozoic, though in most cases the later forms are 

 either distinctly modified, or have reached a higher degree of 

 specialization; and their discussion may be omitted here. Pareia- 

 saurus and Propappus, for instance, from the upper Permian 

 of Russia and Africa, have dorsal osseous scutes, a distinct acromi- 

 al process of the scapula, and coossified calcaneum and astragalus, 

 all unknown in the American Cotylosauria ; characters, which 

 in themselves are sufficient to separate the Pareiasauria as a 

 distinct group. Procolophon, also, with its allies Telerpeton, 

 Sclerosaurus and Koiloskiosaurus from the trias, have departed 

 so far from the primitive simplicity of the earlier types of America 

 in the skull structure and in the pectoral girdle as stated 

 by Huene, that they may well be separated into a group by 

 themselves. Procolophon has been supposed for years, to be a 

 primitive form of the double-arched or 'Diapsidan' type, notwith- 

 standing its occurence in much later deposits than those of Paleo- 

 hatteria. Huene has recently expressed the opinion, one I have 

 had for the past five years, that the Procolophonia have nothing 

 to do genetically with the rhynchocephalian or archaeosaurian 

 phylum. 



Using then the term Permocarboniferous to include the upper 

 carboniferous and lower Permian, and omitting the imperfectly 

 known Archaeosuchus and Eccasaurus, we have perhaps thirty 

 or more genera of undisputed reptiles which it will be of interest 

 to compare directly. 



The first and lowest group of these, the Cotylosauria as usually 

 accepted, began in the upper Pennsylvanian of North America 

 and continued into the Procolophonia of the trias of South Africa 

 and Europe; it has generally been believed to be the order from 

 which all later Amniota have been derived. The second order, 



