KARAGANDOCERATIDS ARE a rare offshoot of the Prionoceratinae,
 resembling that subfamily in general conch form and sutural on-
 togeny, but differing by possession of an acute ventral margin and
 an increasingly trifid ventral lobe.  The systematic position of the
 Karagandoceratidae has been controversial [see Bartzsch and
 Weyer (1988) for an exhaustive review].  The nominate genus,
 Karagandoceras Librovitch, 1940 (type species, K. galeatum),
 possesses a weakly divided ventral lobe which has led authors to
 refer it to both the Praeglyphioceratina (Ruzhentsev, 1960, 1962;
 Bogoslovskii, 1971; Ruzhentsev and Bogoslovskaia, 1978; Bo
 goslovskaia et al., 1999; Kuzina, 2000) and the Goniatitina (Wey-
 er, 1965, 1972; Kullmann, 1981. Discovery of an ancestral kar-
 agandoceratid genus, gen. nov. 1 aff. Karagandoceras Bartzsch
 md Weyer, 1988, in the early Tournaisian Siphonodella sandbergi
 conodont Zone in Germany provided clarification on the proxi-
 mate origin of Karagandoceras and provided a plausible link to
 the early Tournaisian prionoceratin genus Nicimitoceras Korn,
 1993 (type species, Imitoceras subacre Vöhringer, 1960).
 Bartzsch and Weyer (1988) proposed a karagandoceratid phylog-
 eny beginning with gen. nov. I aff.  Karagandoceras in the early
 Tournaisian, progressing through Karagandoceras in the middle
 Tournaisian, and culminating with a third, descendent genus, gen.
 nov. II aff.  Karagandoceras (typical species, Karagandoceras
 bradfordi Manger, 1971), early in the late Tournaisian.  Bartzsch
 and Weyer (1988) elected to leave both the initial and final mem-
 bers of this lineage, gen. nov. I and gen. nov.  II aff.  Karagan-
 doceras, in open nomenclature pending discovery of more com-
 pletely preserved material.  Discovery of superbly preserved rep-
 resentatives of a new species of gen. nov. II aff.  Karagandoceras
 from the Borden Formation in northeastern Kentucky provides
 additional sutural and morphological details that support Bartzsch
 and Weyer's phylogenetic interpretation and makes formal de-
 scription of this terminal karagandoceratid taxon (herein desig-
 nated Masonoceras new genus) possible.