Taxonomy, stratigraphy and phylogeny of the new genus Lanceoptychites (Ammonoidea, Anisian)

For the first time a population analysis of compressed Prychitidae (Ammonoidea) bed-by-bed collected from Prezzo Limestone (Upper Anisian, Southern Alps) is performed. The analysis allows to demonstrate that within some populations of compressed ptychitids during the growth the venter may become subacute/fastigate and the section lanceolate. This modification is not due to growth anomalies, as sometimes believed in literature, bur: is a normal ontogenetic development. The ammonoids with this peculiar ontogeny are moved from the genus Flexoptychites, that groups the com pressed ptychitids with rounded venter, into the new genus Lanceoptychites. The new genus is a secondary descendent of Flexoptychites and comprises 4 species: L, velox (type) sp. n., L. styx sp. n., L. indistinctus (Mojsisovics) and L. charlyanus (Diener). L. styx and its peramorphic descendant L. velox are stratophenetic species. They are described from the Prezzo Limestone, where they are confined to the middle parr of the Paraceratites trinodosus zone (Illyrian). No bed-by-bed information is available for L. indistinctus (Mojsisovics) and L. charlyanus (Diener). These morphospecies are revised on the basis of the type material.