Slit-band gastropods (Pleurotomariida) from the Upper Triassic St. Cassian Formation and their diversity dynamics in the Triassic.

The St. Cassian Formation, Italy, has yielded the most diverse marine invertebrate fauna known from the Triassic. A quarter of all described Triassic gastropod species has been reported from this formation. Most of the gastropod species from the St. Cassian Formation were erected in the 19th century and many of them are known only from their original figures and descriptions. The failure to study type specimens resulted in many erroneous identifications by subsequent authors. Here, we revise the slit band gastropods (Pleurotomariida) from the St. Cassian Formationone of the major groups present in this formation. A total of 77 nominate Pleurotomariida species belonging to 29 genera and 11 families are present in the St. Cassian Formation which comprises approximately 14% of the total nominate gastropod species of that formation. In addition, we revise several taxa that had been wrongly assigned to Pleurotomariida. As other gastropod clades, Pleurotomariida experienced a major extinction at the end-Permian mass extinction event. As in the Late Palaeozoic, their relative abundance in gastropod faunas continued to be 30% in some Anisian faunas but decreased to 510% afterwards. Their diversification at generic level became interrupted by an extinction event within the Carnian, probably by the Carnian Pluvial Event. As a result of their sluggish recovery compared to the other gastropod groups, their species diversity decreased from 26% during the Permian to 18% during the Triassic. Type specimens of the following genera are studied: Proteomphalus, Rhaphistomella, Temnotropis, Kittlidiscus, Stuorella, Schizogonium, Wortheniella, Bandelium, Lancedellia, Rinaldoella, Pseudowortheniella, Paleunema, Ampezzalina, Bandelastraea, Cheilotomona, Pseudoscalites, Delphinulopsis, and Cochlearia. Nine new pleurotomariidan genera are erected: Amplitomaria, Pseudoananias, Lineacingulum, Pressulasphaera, Cancellotomaria, Acutitomaria, Lineaetomaria, Nodocingulum, and Striacingulum. Eight new species are described: Schizogonium undae, Acutitomaria kustatscherae, Wortheniella klipsteini, Wortheniella paolofedelei, Rinaldoella tornata, Nodocingulum ernstkittli, Nodocingulum? turris, and Laubella subsulcata. Eoworthenia frydai is a new replacement name for Worthenia rarissima Barrande.

Middle Permian (Roadian) gastropods from the Khao Khad Formation, Central Thailand: Implications for palaeogeography of the Indochina Terrane.

A new Permian gastropod assemblage from the Roadian (Middle Permian) Khao Khad Formation, Saraburi Group (Lopburi Province, Central Thailand) which is part of the Indochina Terrane, has yielded one of the most diverse Permian gastropod faunas known from Thailand. A total of 44 gastropod species belonging to 30 genera are described herein, including thirteen new species and one new genus. The new genus is Altotomaria. The new species are Bellerophon erawanensis, Biarmeaspira mazaevi, Apachella thailandensis, Gosseletina microstriata, Worthenia humiligrada, Altotomaria reticulata, Yunnania inflata, Trachydomia suwanneeae, Trachyspira eleganta, Heterosubulites longusapertura, Platyzona gradata, Trypanocochlea lopburiensis and Streptacis? khaokhadensis. Most of the species in the studied assemblage represent vetigastropods  (35.6%) and caenogastropods (26.7%) and most of the species belong to Late Palaeozoic cosmopolitan genera. The studied faunas come from shallow water carbonates that are rich in fusulinids, followed by gastropods, ostracods, bivalves and brachiopods. The gastropod assemblage from the Khao Khad Formation shares no species with the gastropod assemblages from other Permian formations in Thailand, the Tak Fa Limestone and the Ratburi Limestone. However, it is similar to the Late Permian gastropod faunas from South China of the Palaeo-Tethys, therefore it suggests that the Indochina Terrane was not located far from South China.