Distinctions between the snake genera Contia and Eirenis

Summary: Various workers have believed Contia to be related to or congeneric with either or both Sonora and Eirenis, the latter a genus of Western Asia. Study of hemipenes, teeth, and jaws indicates that these genera are not related to one another. The hemipenes of Eirenis modesta and Contia tenuis are described. Eirenis is thought to be a derivative of the racer group. Relationships of Contia are unknown. It is suggested that some North American genera with xenodontine-type hemipenes may not be of the South American faunal element and may have been in North America at least as long as the Old Northerners.