NEW APPARATUSES OF THE PENNSYLVANIAN CONODONT GENUS NEOGNATHODUS FROM THE OAK GROVE MEMBER, CARBONDALE FORMATION (DESMOINESIAN), NORTHWESTERN ILLINOIS, U.S.A

Collections from northwestern Illinois, made in recent years by Joseph Pohl of Belgium, Wisconsin, comprise the single best known source of conodont assemblages of the genus Gondolella, the apparatus of which we have described. Associated sparingly with Gondolella are apparatuses of the conodont genus Neognathodus, apparatuses that we previously described on the basis of the then three known apparatuses. The black shale in the Grove Member at two localities in Knox County, northwestern Illinois, has increased this number dramatically and is presently the best, and main, known source of Neognathodus apparatuses. The newly available Neognathodus assemblages suggest that we are dealing with 'normal' ozarkodinid apparatuses, with a probable complement of 14 paired Pa, Pb, M, Sb and Sc elements, associated with a single unpaired Sa element. Specifically, the assemblages appear to be N. medexultimus and possibly N. roundyi, both taxa important in the increasingly utilized Pennsylvanian Neognathodus conodont zonation. Neognathodus apparatuses from the Oak Grove Member, like those of associated conodont taxa, are interpreted as being fecal, as having passed through the gut of a conodontophage. Nevertheless, the arrangement of individual elements in the assemblages is, possibly for biological reasons, much less disturbed and thus more easily interpreted than are the elements of the more common, associated Gondolella. The death arrangement of Neognathodus apparatus elements is more similar to the famous Streptognathodus/Idiognathodus assemblages from the black shales near the top of the Modesto Formation (Missourian) at Bailey Falls, LaSalle County, Illinois.