Passendorferia, Brochwicz-Lewinski, 1973

Cecca, Fabrizio & Savary, Bérengère, 2007, Palaeontological study of Middle Oxfordian- Early Kimmeridgian (Late Jurassic) ammonites from the Rosso Ammonitico of Monte Inici (north-western Sicily, Italy), Geodiversitas 29 (4), pp. 507-548 : 523

?“ Passendorferia ” aff. teresiformis Brochwicz-Lewinski, 1973 ( Fig. 8E )

MATERIAL EXAMINED. — MI4N 8 “top”/5.

STRATIGRAPHICAL DISTRIBUTION. — The specimen has been collected in bed 8d of section Monte Inici East, assigned with doubt to the Hauffianum Subzone of the Late Oxfordian Bimammatum Zone. P. (P.) teresiformis has been reported from older horizons, namely from the Bifurcatus Zone up to lower part of the Bimammatum Zone ( Meléndez 1989).

DESCRIPTION

Evolute shell with subquadrate whorls that do not develop any umbilical wall. The last third of the last whorl, which belongs to the body chamber, shows a subrectangular whorl section with distinctly flat flanks and a rounded large venter. The ornamentation consists of prorsiradiate, sharp biplicate ribs, whose point of branching coincides with the ventrolateral margin. Rib interspaces are as broad as two ribs. The point of branching is elevated and thickened but no real tubercles are developed. Simple ribs are rare. Ribs cross the venter without interruption and develop a gentle adoral convexity. A relatively deep constriction per whorl is visible, though the incomplete preservation prevents the observation of the real number of constrictions. Measurements: see Table 10.

DISCUSSION

The specimen described probably belongs to a new species and its generic position is also uncertain. It resembles to Presimoceras teres (Neumayr, 1873) , which develops only rare biplicate ribs and bears a wider umbilicus, but our specimen is regarded here as a morphologically intermediate form between Passendorferia and Trenerites more than a form close to Presimoceras Sarti, 1990 . It has been compared with P. (P.) teresiformis because of its flat-sided whorls and the sharp ribs that are raised at the ventro-lateral margin. However P. (P.) teresiformis sensu stricto is characterized by a wider umbilicus and less prorsiradiate ribbing. The genus Trenerites Sarti, 1993 includes species of the Platynota Zone (for example T. evolutus (Gemmellaro, 1876) and T. nov. sp. indet. or T. enayi Sarti [in Sarti 1993: pl. 22, fig. 1 and fig. 2 respectively]), whose morphological characters are similar to those developed by our specimen. However, Trenerites is generally more evolute, characterized by narrower whorls and rare bifurcate ribs on the body chamber.

Figures

FIG. 8. — Nebrodites aff. contortus (Neumayr, 1871), specimen MI4N 8d/2 of bed 8d top of section Monte Inici East; A, lateral view; B, ventral view; C, Nebrodites passendorferiiforme Caracuel, Olóriz & Rodriguez-Tovar, 1999, specimen MI4W 10top/2 from bed 10 of section Monte Inici East; D, Nebrodites cf. hospes (Neumayr, 1873), specimen MI4W 10top/3 from bed 10 of section Monte Inici East; E,?“Passendorferia” aff. teresiformis Brochwicz-Lewinski, 1973, specimen MI4N 8 “top”/5 from bed 8d of section Monte Inici East. All figures natural size. Arrows indicate the beginning of the body chamber.