Megastomia sp. 2

(Fig. 8 D1-D3)

MATERIAL EXAMINED. — Sample F11: AMPG (IV) 2563-2569 (seven specimens).

DIMENSIONS. — Maximum height: 2.20 mm.

DISTRIBUTION. — Early Miocene. Proto-Mediterranean Sea: Greece (this paper).

DESCRIPTION

Moderately slender, solid shell; apical angle c. 27°. Partially immersed, type B protoconch. Teleoconch comprising four feebly convex, smooth whorls, with inconspicuous microscopical orthocline growth lines separated by impressed sutures. Last whorl attaining about 60% of total height; slightly angulated at periphery. Columella concave with narrow columellar fold; aperture ovate; outer lip with five observable spiral lines. No umbilicus.

REMARKS

Two protoconch whorls are visible on the shells (including the nucleus). Type B protoconch and columellar tooth place this shell in the Odostomia group, and the spiral striations of the inner lip in the Megastomia genus. It is also separated from ‘ Odostomia ’ sp. 2 of the present material, in having a more immersed protoconch and more rounded whorls.

The overall morphology is similar to M. conoidea with the main difference being that the protoconch of the Greek specimen is of type B a slightly more rounded last whorl. The size and protoconch type coincides with that of Odostomia sp. from the stratotype region of the Aquitanian (Aquitaine Basin, SW France) (Lozouet et al. 2001). Nevertheless, the Greek specimen has a more conical shape and spiral sculpture on the inner lip that differentiates it.