Colpomphalus, Cossmann, 1915

Ferrari, S. Mariel, 2009, Cosmopolitan Early Jurassic marine gastropods from west-central Patagonia, Argentina, Acta Palaeontologica Polonica 54 (3), pp. 449-461 : 452

Colpomphalus ? sp.

Fig. 2B .

Material.—MPEF−PI 1863, poorly preserved teleoconch.

Description.—Small−sized and almost planispiral shell. Protoconch is not preserved. Teleoconch consists of three rapidly expanding whorls with the last whorl incomplete. The adapical portion of the whorls is almost horizontal and slightly concave near the angular edge of the whorls. Sutures are well incised.

Ornament pattern with nodose, spiral and axial elements. The spiral elements consist of weak ribs and two strongly nodose carinae near the suture. The abapical carina forms the peripherical edge; it has fewer and stronger nodes than the adapical carina. Prosocline collabral ribs intersect the spiral elements. The collabral ribs on the lateral flank of the last whorl are orthocline and intersect a weak spiral furrow. Base is not preserved, and apertural and umbilical features are unknown.

Dimensions.—MPEF−PI 1963: maximum height 3.1 mm; maximum width 6.9 mm.

Remarks.—Although important diagnostic characters of aperture and base are not preserved in the present material, the almost planispiral shape, the angular whorls as well as the ornament strongly suggest that this is a species of Colpomphalus .

The South American species, Colpomphalus toarciensis Gründel (2001: 46 , pl.1: 9–13) from the Lower Toarcian of Chile, is similar to Colpomphalus ? sp. Both share a low spira, ornament pattern with spiral ribs and two nodose carinae, and spiral ribs on lateral side of the last whorl. However, C. toarciensis is larger than Colpomphalus ? sp. and has no colabral elements. Moreover, Gründel’s (2001) species has a third row of nodes surrounding the relatively narrow umbilicus. The basal, apertural and umbilical features are not preserved in Colpomphalus ? sp.

Colpomphalus angulati (Quenstedt, 1856) from the Hettangian of Germany ( Gründel 2003: 6, pl. 1: 9, 10) is similar to Colpomphalus ? sp., but the latter differs from the European species in having a more rapidly increasing width and fewer nodes.

Figures

Fig. 2. Early Jurassic gastropods from the “El Córdoba” fossiliferous locality, Chubut Province, Argentina. A. Amberleya? espinosa sp. nov. MPEF−PI 1882, holotype, latex cast of external mold in lateral view (A1, A2), juvenile teleoconch in lateral view (A3), last whorl in lateral view (A4), basal and apertural view (A5), ornament pattern and sutural detail (A6). B. Colpomphalus? sp. MPEF−PI 1863, latex cast of external mold of incomplete teleoconch in apical and lateral view (B1–B3), last whorl ornament detail showing the spiral furrow (B4). C. Striatoconulus sp. MPEF−PI 1867b, latex cast of external mold in apical view (C1), apical detail (C2), first teleconch whorls lateral view (C3). Scale bars 2 mm unless otherwise indicated.