Systematic position of two Early Devonian sinistral heterostrophic gastropods from the Garra Limestone, New South Wales

Two Early Devonian gastropod genera, Garraspira gen. nov. and Anoriostoma from the Garra Limestone, with sinistrally heterostrophic shells, share several shell features and are placed in the new tribe Anoriostomatini within the subfamily Agnesiinae. In contrast to the other members of the latter subfamily these genera represent a lineage in which the apertural slit was lost during evolution. This fact supports the opinion that the presence or absence of the apertural slit does not necessarily have significance for high-level taxonomy. Morphology of the gerontic whorl in Anoriostoma sinistra and Garraspira inusitata suggests their limited mobility during the last ontogenetic stage.