Hesperiella planorbis, Yoo, 1994

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 : 78

Hesperiella planorbis n.sp.

PI. 7 figs 9-13

Description. Shell very small, low spired, sinistral, broadly phaneromphalous. Protoconch coiling inward and hidden by later whorls, but seen in umbilicus, smooth, one and one eighth whorls, apex bulbous. Teleoconch with first I? whorls planispiral, becoming ultradextral, growth lines in early whorls but gradually becoming stronger; collabral lirae above selenizone, opisthocline below selenizone; fine collabral thread extended to umbilicus. Selenizone present from early teleoconch whorl, narrow on periphery. Aperture round; inner and parietal lips thin, outer lip thickened; slit is seen in juvenile shells.

Types. Holotype ( F78402 ) and 3 figured paratypes ( F78403 ). There are 15 unfigured additional specimens ( F78404 ) from the type locality.

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, in upper part of the Dangarfield Formation.

Additional material. 1 specimen from Glenbawn (Locality 31) and 1 from Swains Gully (Locality 25).

Geographic distribution. Swains Gully to Glenbawn.

Geological age. Middle to late Tournaisian.

Etymology. Referring to the planispirally coiled early stage of development of the shell.

Remarks. This species differs from other species of this genus in having a low-spired shell, a very wide umbilicus, and a flattened selenizone. The protoconch and nepionic whorls are planispiral and the early ontogenetic pattern of development is seen through the umbilicus. Two figured paratypes are juveniles.