Platystoma sp. gastropod from the Haragan Formation

In the fossils from the Haragan formation that I have contains a particular type of Gastropod. Pictured below are a couple of examples. I have had a hard time trying to find any information on Gastropods from the Haragan formation but I believe these are Platystoma sp.

Specimen 1

Specimen 2

What I find interesting about the fossil is the way the shell grew rounded along the edges of each whorl rather than having direct contact. Then there the fact that some have a little bit of a spire (such as in specimen 2) while others are more flattened (as in specimen 1). In the Birdsong shale of Tennessee, which is though to be contemporary to the Haragan formation, there is a species called Platystoma ventricosa that looks very similar to the fossils above.

The Haragan formation is thought to be lower Devonian, (Lochkovian stage).