Conodonts from the Late Mississippian Pella beds of south-central Iowa

Conodonts appear to be relatively rare in middle and upper Mississippian rocks and only a few specimens have been described from beds of that general age. A small assemblage has been secured from the type area of the Pella beds in south-central Iowa. The fauna contains representatives of six genera, Cavusgnathus, Gnathodus, Ligonodina, Lonchodina?, Prioniodus, and Spathognathodus. Six new species are established for some of the specimens. Cavusgnathus is the dominant generic element and comprises about half of the collection. Ligonodina and Prioniodus are also common, but the other genera are comparatively rare. These conodonts can best be compared with those known from the Caney shale of Oklahoma. CONODONTS of middle and upper Mississippian age are scarce and comparatively few specimens have been noted or described in the literature. Furthermore, the references are scattered and consist in some cases of only a brief comment or two. Although the fauna under consideration i , by Devonian or lower Mississippian standards (both notable times of abundance) rather sparse, it is nevertheless one of the larger known from the later Mississippian. Pander, the founder of study, was the first (1856) to describe conodonts of possible middle or upper Mississippian age, but the exact horizon or horizons of the occurrences are uncertain. In 1900, Hinde described a small number of conodonts obtained from rocks of various ages and at several localities in the Carboniferous of western Scotland. Roundy (1926) illustrated and described a few conodonts from the Barnett shale of central Texas-strata which carry the goniatite genera Eumorphoceras, Goniatites, Girtyoceras, and others which date the beds as about Meramec in age. A paper by Hermann Schmidt in 1934 called attention to the presence of conodonts in the Lower Namurian of Westphalia in the zone of Eumorphoceras bisulcatum. Schmidt did not treat the conodonts in detail and as individual specimens but regarded them as forming assemblages-that is, several different genera and species of conodonts were presumed to have been derived from a single organism. Each of these assemblages was named and Schmidt related them to fishes. Later the same year, Scott, writing on the possible zoological relationships of conodonts, illustrated specimens from the Heath formation (late Mississippian) of Montana. He, like Schmidt, treated the conodonts as assemblages, and, incidentally, concluded that they were probably annelid remains. Relatively the most extensive treatment of late Mississippian conodonts has been by Branson and Mehl. In 1941 they stated that the Caney shale of Oklahoma (p. 167) seems to contain conodonts in fair abundance in one or more zones, and they described and illustrated about 40 specimens. In this same paper Branson and Mehl indicate (p. 168) that they also had some conodonts from the Pitkin limestone of the same general region; four of these Pitkin conodonts were later illustrated and described by Branson and Mehl (1941b) as syntypes of a single species of Spathognathodus. Also in 1941, E. B. Branson and C. C. Branson (p. 131) in a discussion of the stratigraphy of the Wind River Mountains of western Wyoming noted that a conodont fauna was recently discovered [in the Sacajawea formation] and is being studied. These authors apparently regarded the Sacajawea as either of Chester age or slightly older. What appear to be the youngest: Mississippian conodonts so far described are those secured by C. L. Cooper (1947) from upper Kinkaid beds at the top of the Chester in southwestern Illinois. About a dozen conodonts were illustrated and described in a paper dealing