THE UPPER PENNSYLVANIAN (MISSOURIAN) AMMONOID PENNOCERAS FROM THE NORTH AMERICAN MIDCONTINENT

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Until recently considered a rare Appalachian Basin endemic, Pennoceras Miller and Unklesbay, 1942 has emerged as one of the most widespread and locally abundant ammonoids in the lower Missourian of the Midcontinent (Boardman et al., 1994). Here we document the first Midcontinent record of the type species of Pennoceras , P. seamani Miller and Unklesbay, 1942, from the Hushpuckney Shale equivalent in southeastern Kansas. Additional, previously undescribed species of Pennoceras from the Exline Limestone and Mound City Shale equivalents in Oklahoma and southeastern Kansas are described as Pennoceras bennisoni new species and Pennoceras heckeli new species. Discovery of these ancestral species provides clarification on the derivation and early history of Pennoceras and provides a possible link to the Desmoinesian Wiedeyoceratidae. Dimensions D, H, W, and U represent conch diameter, corresponding whorl height and width, and umbilical diameter measured from seam to seam. Suture terminology is that of Ruzhencev (1960); V, L, U, I, and D represent the ventral lobe, lateral lobe, umbilical lobe, internal lateral lobe, and dorsal lobe. Sutural symbols hs, hl, and wl refer to height of secondary ventral saddle and height and width of entire ventral lobe, respectively. Repository abbreviations are: SUI, University of Iowa; CM, Carnegie Museum of Natural History. ### Type species Pennoceras seamani Miller and Unklesbay, 1942. ### Included species Pennoceras bennisoni n. sp.; Pennoceras heckeli n. sp. ### Emended diagnosis Conch small (30–35 mm at maturity), subglobose to globose (W/D 0.55–0.9) with depressed to equidimensional whorls (H/W 0.6–1.0) and closed umbilicus. Fine to coarse, straight transverse lamellae trace a low ventral salient. External suture comprises wide ventral lobe with low median saddle ( hs / hl about 0.4) and short, rounded or bluntly pointed ventral prongs; broadly rounded lateral saddle; symmetrical, narrowly rounded or bluntly pointed lateral lobe; and small, rounded umbilical lobe. Sutural formula: ( V1V1 ) …