Chesterian davidsoniacean and orthotetacean brachiopods, Ozark region of Arkansas and Oklahoma

Abstract

Three species of orthotetaceans and one species of davidsoniacean are among the strophomenid brachiopods from Chesterian (Upper Mississippian) rocks of northern Arkansas and northeastern Oklahoma. Type material from the Fayetteville Shale, Orthotetes subglobosus and O. subglobosus var. protensus, is figured for the first time. We regard these species, and O. subglobosus var. batesvillensis Girty from the Batesville Sandstone, as distinct species, for which we are selecting lectotypes. We describe a fourth species, O. stenopsis n.sp., from the Pitkin Limestone. Another species, described from the Pitkin as Streptorhynchus suspectum, has an impunctate shell and is thus not an orthotetacean. This bizarre species generally has a long twisted beak, high interarea, and large forked cardinal process; a myophragm may occur in either valve, but more commonly is in the brachial valve alone. We designate a lectotype for this species and propose a new genus Adectorhynchus and a new family Adectorhynchidae, under the Davidsoniacea, for this taxon.