Three genera of gastropods described from the Lower Devonian Rockhouse Formation of Hardin County, Tennessee, currently are considered to be junior subjective synonyms of Platyceras (Visitator) Perner, 1911. Evaluation of the type specimens of these genera as well as types of two other gastropods from the same formation reveals the following: Platyostoma quadrangulare (Dunbar, 1920) is the only platyceratid gastropod among them; Saffordella tennessensis Dunbar, 1920 has a selenizone above midwhorl so it is an eotomarioidean belonging to the Gosseletinidae; Aulopea nelsoni Dunbar, 1920 and the lectotype of Distemnostoma princeps Dunbar, 1920 each has a broad subsutural sinus on the upper whorl surface similar to the Omphalotrochidae, as well as a basal sinus similar to certain primitive caenogastropods, so their systematic position is uncertain; I consider Holopea planidorsata Dunbar, 1920 to be a juvenile specimen of D. princeps; the fragmentary paralectotype of D. princeps possibly represents a gerontic form of Distemnostoma curtum Dunbar, 1920, which possesses a well-developed selenizone on an upwardly projecting shoulder at the edge of the upper whorl surface. Because D. curtum appears to be unrelated to D. princeps, the genotype of Distemnostoma, I propose the new generic name Omocordella for D. curtum. The new family Micromphalidae is erected to include Ordovician Slehoferia Rohr and Fryda, 2001, lower Carboniferous Micromphalus Knight, 1945, and Omocordella n. gen.