Cyclothyris americana Cooper is recorded for the first time from the Texas Lower Cretaceous (Glen Rose Formation, probably lower Albian) in Hays County. Lamellaerhynchia viae n. sp. is described from the Main Street Formation (probably basal Cenomanian) in the Fort Worth and Waco areas. Relationship of the two genera is discussed; Lamellaerhynchia is probably the direct ancestral form. Cyclothyris is interpreted as an inhabitant of shallow, rough water.