Resumen
A new species of Steinmanella Crickmay, which belongs to the subgenus Macrotrigonia Camacho y Olivero, is described in this paper. The new taxon is named Steinmanella (Macrotrigonia) pehuenmapuensis sp. nov., and was found in the lower part of the Agrio Formation (Hauterivian) from cerros Mesa and Negro, Covunco creek area, Neuquén Province, Argentina. Some specimens of this new species were previously ascribed to 'T.' vacaensis Weaver by former authors. However, it clearly differs in having a much longer and straight anterior margin forming with the ventral margin an almost 90° angle, and a larger height-length ratio. On the other hand, S. (M.) pehuenmapuensis sp. nov. occurs in association with invertebrates of the Lyticoceras pseudoregale Zone, and its age can be regarded as Lower Hauterivian, whereas S. (M.) vacaensis (Weaver) is relatively younger in age, as it has been recorded in upper levels within the Agrio Formation. Therefore, a case of intraspecific variability between both species is discarded. Considerations about the content and taxonomic status of the genus Steinmanella Crickmay are also made.