Perisphinctes (Dichotomosphinctes), 1926

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 : 518-520

Perisphinctes (Dichotomosphinctes) gr. antecedens ? Salfeld, 1914 ( Fig. 5C )

MATERIAL EXAMINED. — MI3 9/3, MI3 9/10.

STRATIGRAPHIC DISTRIBUTION. — Bed 9 of section Castello Inici, which has been assigned to the Middle Oxfordian Plicatilis Zone.

DESCRIPTION

The two incomplete specimens correspond to evolute shells; the largest one probably reached the

diameter of 12 cm. The whorl section is rectangular to subtrapezoidal, characterized by a relatively large venter, flat to gently round flanks, a well developed rounded umbilical margin and a flat to oblique umbilical wall. Ribs are strong and gently prorsiradiate. The two fragments only show biplicate ribs whose point of branching is located on the upper fourth of the flank.

DISCUSSION

The preservation of the studied specimens is too poor to allow a reliable identification. The ribbing and the general features of the shell suggest affinities with the group of P. antecedens . The specimens from Castello Inici bear a wider whorl section than the one developed by the type specimens studied by Arkell (1937) and by specimens from the Jura Mountains and from Beauvoisin ( France), respectively described by Enay (1966) and Bourseau (1977). However, Enay (1966: 473) mentions that some specimens have flanks that converge towards the venter.

Figures

FIG. 5. — A, B, Taramelliceras cf. hauffianum? (Oppel, 1863), specimen MI4W 8b/c/3 from bed 8c of section Monte Inici East: A, lateral (slightly oblique) view; B, ventral view; C, Perisphinctes (Dichotomosphinctes) gr. antecedens? Salfeld, 1914, specimen MI3 9/10 from bed 9 of section Castello Inici; D, Subdiscosphinctes sp., specimen MI4N 9/4 from bed 9 of section Monte Inici East. All figures natural size. Arrows indicate the beginning of the body chamber.