Field research connected with the revisional study of the large Liassic Lamellibranchia, characteristic of the "Lithiotis" facies, has permitted the identification of the subgenus Isognomon (Mytiloperna) v. Ihering 1903 and the genus Gervilleioperna Krumbeck 1923. Both are Lamellibranchia with a multivincular ligament. Mytiloperna was first identified in the Liassic of Chile; then it was noted in the Middle Jurassic of various European localities, and it has been recently recorded from the Liassic of Japan. Gervilleioperna has been identified in the Liassic of Timor and Marocco. In many cases, the original structure and chemical composition are conserved in the shells which were collected near Ponte Anguillara (Verona, Italy). The presence of aragonite in the shells of both taxa has been verified through roentgenographic analysis by the Debye-Scherrer method. Gervillia ombonii Negri 1891, a species already identified in Veneto Lias, is referred to the genus Gervilleioperna Krumbeck. With respect to the species of Gervilleioperna Krumbeck from Marocco, only part of the Gervilleioperna atlantis Dubar specimens (1948) may be considered valid. The specific classification of Mytiloperna requires the collection of additional specimens. The morfological description of the two taxa is accompanied by information regarding their recognition in the field.
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Con il contributo del Ministero per i Beni e le Attività Culturali