Orthosphinctes (O.) aff. fontannesi ( Choffat, 1893 )

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 : 538-540

Orthosphinctes (O.) aff. fontannesi ( Choffat, 1893) ( Fig. 13B )

MATERIAL EXAMINED. — MI4N 8 “top”/3. STRATIGRAPHIC DISTRIBUTION. — The specimen has been collected in bed 8d of section Monte Inici East, which has been assigned with doubt to the Hauffi- anum Subzone of the late Oxfordian Bimammatum Zone. O. (O.) fontannesi has been reported from older layers, namely from the lower part of the Bimam- matum Zone by Olóriz et al. (1999) and Caracuel et al. (2000).

DESCRIPTION Evolute shell with an ovate, compressed whorl section. The umbilical wall is low, the umbilical edge is rounded and whorl flanks converge towards the venter. The ornamentation is poorly visible in the details and it mainly consists of biplicate and intercalatory ribs; simple ribs rarely occur. In the last quarter of the last whorl two constrictions are visible: the adapical one is deep and oblique to ribbing, the second is shallow and almost parallel to ribbing. The mouth is not preserved and no traces of suture line are visible. It is therefore impossible to recognize whether the specimen is entirely septated or not. Measurements: see Table 24.

DISCUSSION

The identification of this specimen is difficult because of its insufficient preservation. It is impossible to state whether it is a microconch or an immature macroconch because any traces of the suture line are visible. From a pure morphologic point of view it shows some morphological similarities with O. (O.) fontannesi ( Choffat 1893: 40, specimens figured in pl. 9, figs 1 and 3 only). However, with respect to our specimen, this species shows finer ribs, a wider umbilicus and a different position of the constrictions in the last whorl. At a comparable diameter O. (O.) mogosensis ( Choffat 1893: 50, pl. 12, figs 5-8) has a narrower umbilicus and a slightly narrower ventral area.

Figures

FIG. 13. — A, Orthosphinctes (Orthosphinctes) tiziani (Oppel, 1863), specimen MI4N 8 “top”/11 from bed 8d of section Monte Inici East; B, Orthosphinctes (Orthosphinctes) aff. fontannesi (Choffat, 1893), specimen MI4N 8 “top”/3, from bed 8d of section Monte Inici East; C, Orthosphinctes (Ardescia) betica Caracuel, Olóriz & Rodriguez-Tovar, 1999, specimen MI4N top10/1 from bed 10 of section Monte Inici East. All figures natural size. Arrows indicate the beginning of the body chamber.