Low to moderately highly-diverse ostracode assemblages containing a total of 49 taxa occur in the Imo Formation (Mississippian, Chesterian) in north central Arkansas. The less diverse assemblages are dominated by the platycope Cavellina, while the more diverse are dominated by the palaeocopes Hollinella, Gortanella, Amphissites, Sargentina, and Deloia; the leiocopes Proparaparchites and Shivaella; and the metacopes Healdia and Healdioides. The change in assemblages up section in the central portion of the formation indicates a deepening of water with variations in the amount of influx of terrigenous clastics in a nearshore marine environment.
New taxa described include Aechminella prostata, Cornigella laterispinosa, Hollinella (H.) imoensis, H. (H.) denotata, Pseudokegelites dorsopeltatus new genus and species, Polytylites oblongus, Glyptopleuroides inregularis, Oliganisus amictus, Doricranos incohatus new genus and species, Knoxina sohni, Proparaparchites ignotus, Shivaella juxarecta, Orthobairdia redacta, Monoceratina arkansasana, Healdioides retusus, H. commensuratus, Seminolites orthapsis, Venula elegantula, Prodigious rostratus new genus and species, and Microcheilinella? lenticularis.