Gyronema nacre/ormis

Yoo, E. K., 1994, Early Carboniferous Gastropoda from the Tamworth Belt, New South Wales, Australia, Records of the Australian Museum 46 (1), pp. 63-120 : 81-82

Gyronema nacre/ormis n.sp.

PI. 10 figs 6-10

Description. Shell small, moderately high-spired turbiniform, narrowly phaneromphalous. Protoconch simple, seemingly smooth, with a sharp boundary between protoconch and teleoconch. Teleoconch consisting of 2 layers with nacreous lining on inner surface with whorl profile moderately arched, suture moderately deep, first 11,4 whorls smooth with growth lines very faint remainder of teleoconch with spiral lirae, 15 in the final whorl, growth lines obscure. Aperture suboval, with finer lip thin, straight to slightly arcuate, reflexed, anterior end somewhat extended; outer lip thin with a shallow sinus.

Types. Holotype ( F78425 ), 1 figured paratype ( F78426 ) and 9 unfigured paratypes ( F78427 ).

Type locality. 150 m west of 'Marohn' homestead, on the Scone-Gundy roadside, 4 km south-west of Gundy, NSW (Locality 28).

Stratigraphic position. In bioclastic limestone, upper part of the Dangarfield Formation.

Additional material. 10 specimens from Swains Gully (Locality 25).

Geographic distribution. Swains Gully to 'Marohn'.

Geological age. Middle to late Tournaisian.

Etymology. Referring to the nacreous internal surface layer of the shell.

Remarks. Gyronema nacre /ormis n.sp. is characterised by having a double layered shell with nacreous inner lining, which is commonly seen in Recent species of Trochidae . The shell surface is generally buff in color, but the original nacre is observed on the inner surface of a number of specimens. Gyronema nacre /ormis differs from the type species, Gyronema subsinuata (Meek & Worthen) , in lacking parietal inductura. The tall, smooth protoconch and absence of selenizone preclude this form from the pleurotomarioidean gastropods.