Key points are not available for this paper at this time.
Nevadia is the earliest and the most primitive member of theMesonacidæ, and as shown by Walcott may be regarded as representing the ancestral type of this family. The same authorityshows that the Paradoxidæ have descended from the Mesonacidæ. Redlichia also exhibits features which link it with the Paradoxidæ and the Mesonacidæ.
H. H. Swinnerton (1915) studied this question.