﻿AbstractRecent fossil shell mining for a new rail line in the Orlando area of Orange County, Florida has uncovered two species of the ellobioid genusCarychiumO. F. Müller, 1773 in a bed of freshwater marl from the Lower Pleistocene Nashua Formation. To taxonomically interpret these finds, the well-preserved shells were imaged via high-resolution X-ray tomography (micro-CT) to view significant internal diagnostic characters such as the columellar configuration and the degree of lamellar sinuosity and their relationship in context to the entire shell. The image data are compared to that of type material and extant and fossilCarychiumspecies inhabiting the SE USA, Mexico, Central America, and Jamaica. Based on these results, the speciesCarychiumfloridanumG. H. Clapp, 1918 andCarychiumnashuaensesp. nov.are identified from fossil shells dating from the Early Pleistocene. This work documents the first fossil members ofC.floridanumand the first fossilCarychiumfrom the SE USA.