Redescriptions of some Lower Devonian gastropods from Tennessee currently considered to be platyceratids

Abstract

AbstractThree genera of gastropods described from the Lower Devonian Rockhouse Formation of Hardin County, Tennessee, currently are considered to be junior subjective synonyms ofPlatyceras(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 tennessensisDunbar, 1920 has a selenizone above midwhorl so it is an eotomarioidean belonging to the Gosseletinidae;Aulopea nelsoniDunbar, 1920 and the lectotype ofDistemnostoma princepsDunbar, 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 considerHolopea planidorsataDunbar, 1920 to be a juvenile specimen ofD. princeps; the fragmentary paralectotype ofD. princepspossibly represents a gerontic form ofDistemnostoma curtumDunbar, 1920, which possesses a well-developed selenizone on an upwardly projecting shoulder at the edge of the upper whorl surface. BecauseD. curtumappears to be unrelated toD. princeps, the genotype ofDistemnostoma, I propose the new generic nameOmocordellaforD. curtum. The new family Micromphalidae is erected to include OrdovicianSlehoferiaRohr and Fryda, 2001, lower CarboniferousMicromphalusKnight, 1945, andOmocordellan. gen.