NEW AND LITTLE-KNOWN GASTROPODS FROM THE ALBIAN OF THE MAHAJANGA BASIN, NORTHWESTERN MADAGASCAR

Abstract

Thirty-one gastropod species and one type of isolated larval shell are described from a quarry near Ambatolafia in the Mahajanga Basin, northwestern Madagascar. The ammonite fauna indicates a lower Albian age of the fauna (Cleoniceras besairiei Zone). The taxonomic position of the species described earlier is reviewed, incorporating new data on shell structure and protoconch morphology. Twelve species and one genus are new, with four species described in open nomenclature. The oldest hitherto known representatives of Cocculina sensu lato, Iphitus, Conjectura, Entomope, Tomura, and possibly Vatopsis and Paladmete, are described. Nacre is documented in a species of Semisolarium, providing further evidence for the position of this genus within the Vetigastropoda. Eight of the species occur also in the Cretaceous of Europe or are tentatively assigned to European species. Three species have close relatives in the Aptian/Albian of Japan, one species may have relations to the Albian of Texas. The new genus is Mahajangina (family uncertain) for a species having a small, trochispiral teleoconch with spines on the periphery, and a conical, bicarinate larval shell. The new species are: Cirsocerithium collignoni, Zardinistylus betsibokaensis, Pommerozygia mahajangensis, Conjectura minuta, Buvignieria berwaldi, Mahajangina weitschati, Entomope crassilabrum, Paladmete? rasoarinoroae, Tomura ambatolafiensis, Carinathilda parviruga, Carinathilda bandeli, and Gymnothilda pagodoidea.