RE-EVALUATION OF VALVATA? MONTANAENSIS MEEK AND THE OVERBURDENED VALVATA MÜLLER

In a number of ways, North American Cretaceous continental mollusks represent an understudied group that limit their potential utility. Taxonomic work has yet to rectify the traditional approaches used to name new species during groundbreaking and subsequent geological and paleontological studies in the exploration of the Western Interior. Use of extant genera and syntype typology promoted poor diagnoses, resulting in Lazarus/Elvis taxa surviving multiple epochs of significant environment change. As evidence shows (Hartman and Bogan, 2009), problems arose from applying extant taxon records to deep time fossil lineages occurring across extinction boundaries. A typical example is the Campanian Valvata? montanaensis Meek, 1876. We 1) consider the placement of the species in the family Valvatidae (Valvatoidea, Lower Heterobranchia); 2) choose a lectotype specimen for V.? montanaensis, as no holotype was selected by Meek; 3) interpret Meek’s specimen measurements; 4) evaluate the stratigraphic horizon of its occurrence; and 5) evaluate other relevant fossil taxa assigned to Valvata and related genera. Results of the analysis include the following: 1) proposal of a new genus, with V.? montanaensis as its type species. 2) USNM-PAL 2177a selected as lectotype for the species, as it best exhibits the defining traits of the new nomenclatural combination, possessing a slightly enclosed umbilicus, depressed spire, complete peristome and angular whorl margin. 3) USNM 2177c most closely matches the measurements given by Meek (1876, t-f. 82), although current measurements of the text-figure match USNM 2177a. Meek’s measurements of V.? montanaensis are slightly larger in height and smaller in width (~6% in both dimensions) than recent measurements of USNM 2177c. 4) Information gleaned from Stanton and Hatcher (1905) suggests the species is from the upper part of the Judith River Formation in the type area (Coal Ridge Member, Rogers et al., 2016). 5) Mid Jurassic V. delaunayi Cossman and Late Jurassic V. leei Logan are preliminary assigned to New Genus S, delimiting a biorange of Mid Jurassic to Late Cretaceous.