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S. W. WILLISTON 



the alveolar margin of the teeth toward the symphysis, and often 

 bearing teeth. The prearticular forms the inner border of the 

 meckelian orifice and is intercalated between the coronoid and 

 splenial anteriorly. The splenial takes part in the mandibular 

 symphysis, and is more or less visible on the outer side of the 



Fig. 14. — Dimetrodon, sp.: Right mandible, from inner side. Explanations as 

 in Fig. 13. 



Fig. 15. — Labidosaunis hamatus Cope: A, right mandible, inner side; B, the 

 same, outer side. Explanations as in Fig. 13. 



mandible. A posterior inframeckelian foramen is present in the 

 most primitive reptiles. 



These characters I have determined in six different genera of 

 Permian reptiles, and I doubt not that they will be found in all, 

 from the Lower Permian at least. Figures of the mandibles of 

 four of these are given herewith, and do not need detailed descrip- 

 tion {Dimetrodon, Figs. 13, 14; Casea, Fig. 9; Lahidosaurus, 



