Perisphinctes bocconii, (Gemmellaro, 1871)

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 : 520-521

Sequeirøosia bocconii ( Gemmellaro, 1871) ( Fig. 6 )

Perisphinctes bocconii Gemmellaro, 1871: 156 , pl. 20, fig. 2.

? Perisphinctes bocconii – Gemmellaro 1874: 5, pl. 2, fig. 2.

Non Perisphinctes bocconii – Gemmellaro 1877: 91, pl. 4bis, fig. 15.

Sequeirosia (Sequeirosia) bocconii – D’Arpa & Meléndez 2002: 275, figs 187, 188.

MATERIAL EXAMINED. — MI4W 6c/3.

STRATIGRAPHIC DISTRIBUTION. — The specimen has been collected in bed 6c of section Monte Inici East, which has been assigned to the Middle Oxfordian Transversarium Zone. D’Arpa & Meléndez (2002) assumed that the

vertical distribution of this species could correspond to an intermediate horizon between the Antecedens and Luciaeformis subzones, most probably the base of the Transversarium Zone. However, the precise stratigraphic position of Gemmellaro’s specimens remains unknown.

DESCRIPTION

Large evolute, serpenticone shell, which is represented by an incomplete whorl that seems to belong to the body chamber. The whorl section is subrectangular from a diameter of about 190 mm. The umbilical wall is not visible due to poor preservation; the venter and the umbilical margin are rounded, flanks are flat and almost parallel in the first half of the last whorl to become convergent towards its end. Primary ribs are strong, long, rounded, slightly prorsiradiate, irregularly spaced. The bifurcation of the ribs is not clearly visible because of the bad preservation. Ribs seemingly weakened on the venter and become more spaced towards the very last portion of the whorl. Measurements: see Table 7.

DISCUSSION

The lack of inner whorls makes the identification of this single specimen quite difficult. However, the general characteristics of both the shell and its sculpture strongly suggest its identification with S. bocconii . Similar forms already assigned by Gemmellaro to S. bocconii (1877: pl. 4bis, fig. 15) have been excluded from this species by Cecca et al. (2001) and then by D’Arpa & Meléndez (2002) who assigned them to Passendorferia pl. sp. indet. Our specimen resembles more the one from Ciacati Roccapalumba selected by D’Arpa & Meléndez (2002) as the lectotype of the species than the specimen collected in the locality “Chiusa e Palazzo-Adriano” figured by Gemmellaro in 1874. However, it is more evolute than the lectotype. There are also morphological resemblances with the specimen that Meléndez (1989: pl. 16, fig. 1) has figured with the name Sequeirosia (S.) n. sp. A.

Figures

FIG. 6. — Sequeirosia bocconii (Gemmellaro, 1871), specimen MI4W 6c/3 from bed 6c of section Monte Inici East. Scale bar: 5 cm.