These were seen at muck sites at night. Although the shape of the shell looks to me more like a Casmaria erinaceus, the adult specimen below is a very close match to Casmaria ponderosa in Poppe (2008) (pl. 28, fig. 1). We did not examine the aperture's outer lip for the pointed denticles that distinguish C. ponderosa from C. erinaceus.
Juvenile shell below.
Created 11 February 2020
Updated 5 October 2022