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Holcoptychites is known only from the Neuquén Basin, Argentina, but appears close to the more widespread genera Jeanthieuloyites and Spitidiscus. Thus it is placed in the subfamily Spitidiscinae (Family Holcodiscidae). Previously described Holcoptychites species are revised and their taxonomy clarified, while one new species is left under open nomenclature. The sequence of forms allows two subzones to be recognized. These are correlated provisionally with the lowest Hauterivian Acanthodiscus radiatus Zone of the Mediterranean region. Fil: Aguirre-Urreta, Maria Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina Fil: Rawson, Peter F.. Colegio Universitario de Londres; Reino Unido

Hoplitocrioceras is a poorly-known ammonite genus of late Early Hauterivian age that may be endemic to the Neuquén Basin Argentina where it occurs at a clearly defined horizon in the Agrio Formation. It is an unusual genus with uncoiling (crioceratitid) whorls that remain linked by a thick dorsal shell that drapes over the tips of sharp upwardly-pointing ventro-lateral spines. It has been interpreted as either a necomitis or a crioceratitid but is here regarded as one of the last members of the Family Neocomitidae. One new species is proposed: H. giovinei. Fil: Aguirre-Urreta, Maria Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina Fil: Rawson, Peter F.. Colegio Universitario de Londres; Reino Unido

The olcostephanid fauna of the Olcostephanus (O.) laticosta [formerly O. (O.) leanzai] Subzone (Agrio Formation) represents the last of four discrete invasions of olcostephanid ammonites into the Neuquén Basin of west-central Argentina. Olcostephanus (O.) laticosta (Gerth) dominates the fauna and is known only from the Neuquén Basin. But the co-occurrence of the distinctive subgenus Feannoticeras, newly recorded from Argentina, provides a link with the 'standard' West Mediterranean sequence and indicates that the O. (O.) laticosta Subzone is probably of mid Early Hauterivian age. This is supported by the discovery of two specimens of the widely distributed late Early Hauterivian species O. (O.) variegatus (Paquier) in the overlying Hoplitocrioceras giovinei Subzone. O. (Jeannoticeras) agrioensis sp. nov. is described. Fil: Aguirre-Urreta, Maria Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina Fil: Rawson, Peter F.. Colegio Universitario de Londres; Reino Unido