Abstract
Three species ofKarakaschiceras, K. attenuatus(Behrendsen, 1892),K. neumayri(Behrendsen, 1892), andK. lycoris(Leanza and Giovine, 1949), and one species ofNeohoploceras, N. arnoldi(Pictet and Campiche, 1860), are described and figured from the Valanginian strata of the Neuquén basin in west-central Argentina. The large collection of fossils available for study shows wide intraspecific variation regarding ornament and whorl section inKarakaschiceras neumayriandNeohoploceras arnoldi, casting some doubts on the current systematics applied to species of these genera. The biostratigraphic position of the four species in the Neuquén basin corresponds to theKarakaschiceras attenuatusSubzone of theOlcostephanus atherstoniZone. This subzone is correlated with the MediterraneanKarakaschiceras inostranzewiandSaynoceras verrucosumzones of Europe at the base of upper Valanginian sections.
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