The extinct Nerineoidea and Acteonelloidea (Heterobranchia, Gastropoda): a palaeobiological approach Author Kollmann, Heinz A. text Geodiversitas 2014 2014-09-26 36 3 349 383 http://dx.doi.org/10.5252/g2014n3a2 journal article 6397 10.5252/g2014n3a2 5dd903f5-b398-4a17-83e5-364766291411 1638-9395 4538503 Subfamily PTYGMATIDINAE Pchelintsev, 1960 ( Fig. 3A, B, I ) Ptygmatidinae Pchelintsev, 1960: 51 . Bactroptyxisidae Pchelintsev, 1965: 96 . TYPE GENUS. — Ptygmatis Sharpe, 1850 ( 1850: 104 ) . TYPE SPECIES. — Pt. bruntruntana Thurmann, 1832 ( 1832: 17 ) . SUBFAMILY CHARACTERS . — Broad umbilicate to anomphalous. Whorls flat to moderately concave, rhombic in cross section.Two columellar plaits extending to detached columellar inductura. Parietal and palatal plait thin in the last whorl. External end of plaits inflated, truncated or bifurcate in earlier whorls, incisions between columellar plaits deep and bent. REMARKS The internal plaits are delicate in the final whorl but may become increasingly complex by the deposition of additional shell material in earlier whorls ( Fig. 3F, I ). According to Wieczorek (1998) all transitions are visible, even on the species level. Hudlestone (1889) records Ptygmatidinae taxa from the Inferior Oolite (Middle Jurassic) ranging in outline between slender and moderately broad. The increase of the apical angle accompanies a broadening of the columella cavity. The transitions are fluent and there is no reason to distinguish the Bactroptyxisidae Pchelintsev, 1965 upon species with solid columellas.