Gregoryceras cf. defayi Bert, Marchand, Gygi & Delanoy, 2003

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 : 529

Gregoryceras cf. defayi Bert, Marchand, Gygi & Delanoy, 2003 ( Fig. 9D)

MATERIAL EXAMINED. — MI3 9/8.

STRATIGRAPHIC DISTRIBUTION. — Bed 9 of section Castello Inici, which has been assigned to the Middle Oxfordian Plicatilis Zone. According to Bert (2004), the distribution of G. defayi is limited to the Middle Oxfordian Plicatilis Zone and in particular to the lower part of the Vertebrale Subzone.

DESCRIPTION

The fragment collected at Castello Inici shows a large, subcircular whorl section. The flanks are rounded; the umbilical wall is large and oblique, passing to a rounded umbilical margin. No traces of sculpture are visible up to 20 mm. The preserved fragment of the last whorl shows strongly rursiradiate ribs. No sculpture is visible on the umbilical wall of the last whorl.

DISCUSSION

Despite the strongly incomplete preservation, this specimen can be compared with G. defayi . G. tenuisculptum Gygi, 1977 differs because of its shorter smooth initial stage. Gregoryceras iteni (Jeannet, 1951) bears ventrolateral thickenings which are not visible in our specimen.