Lissoepikodus nudus gen. et sp. nov. and Oepikodus cleftus sp. nov., new septimembrate conodont taxa from the Early Ordovician of Australia and Nevada

Two new species of the Early Ordovician (early Arenig) conodont family Oepikodontidae, belonging to the genera Oepikodus Lindström and Lissoepikodus gen. nov., are described from material collected in Australia and Nevada. The species are Oepikodus cleftus sp. nov. and Lissoepikodus nudus gen. et sp. nov. A septimembrate apparatus structure is recognized for each of these species. Species assigned to the genera Oepikodus and Lissoepikodus can be distinguished from species of the genera Baltoniodus and Prioniodus by the presence of a quadriform alate Sa element rather than a triform alate Sa element. The evolutionary relationship and the biostratigraphy of these species are briefly discussed. The terms biform, triform, and quadriform are introduced to define the process morphology of the symmetrical alate Sa element of the conodont apparatus.