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Seven graphs analyze the important dimensions and proprtions of the premolars in the described species of Osteoborus and Borophagus. Grids or scales of standard deviation multiples for a standard population (Coffee Ranch) are superimposed on the graphs. A graph of the relative width of P/4 plotted against the absolute width of M/1 shows, among other things, that Aelurodon validus does not belong in Osteroborus. The graphs show exactly the relations of isolated specimens and types to each other but do not resolve completely the fundamental uncertainties regarding their species or biostratigraphic positions. Species, as presently constituted, may differ less than extreme variants of the standard population. A probable new "missing link" between Osteoborus and Borophagus was found in the Christian Ranch local fauna of Texas. Both Osteoborus and Borophagus seem to have produced aberrant species. The early evolution of Osteoborus may be deciphered only by further study involving both Aelurodon and Tomarctus.