. Bulletin of the British Museum (Natural History). Fig. 319 Worldwide Palaeogene distribution of Mytilopsis. -k, Eocene record; #. Oligocene records. accommodated species with shapes rather similar to the 'mytiliformes' and included (1897: 175) several European Tertiary species such as Dreissena sowerbyi d'Orbigny, 1850 (Figs 316-318) from the Headon Beds of the English Eocene (Priabonian Stage). A re-examination of the type and other material of this species shows that it is not generically separable from Mytilopsis. Unnamed specimens in BMPD from Aquitanian and other mid-Tertiary
. Bulletin of the British Museum (Natural History). Fig. 319 Worldwide Palaeogene distribution of Mytilopsis. -k, Eocene record; #. Oligocene records. accommodated species with shapes rather similar to the 'mytiliformes' and included (1897: 175) several European Tertiary species such as Dreissena sowerbyi d'Orbigny, 1850 (Figs 316-318) from the Headon Beds of the English Eocene (Priabonian Stage). A re-examination of the type and other material of this species shows that it is not generically separable from Mytilopsis. Unnamed specimens in BMPD from Aquitanian and other mid-Tertiary horizons in France and Germany, as well as German material identified by D. Kadolsky (personal communication) as Mytilopsis brardi (Brongniart, 1823), confirm the basic soundness of Andrus- sov's observations. It thus becomes apparent that Mytilopsis was far from rare in the European early to mid-Tertiary, and definitely occurs in the Upper Eocene of England. It also appears that during the late Neogene, Mytilopsis is replaced by Dreissena in Europe. This is in complete contrast to the generally accepted view that the European fossil species should all be placed in the living genus Dreissena, which allegedly first occured in the Eocene, whilst western hemisphere dreissenids should all be assigned to Mytilopsis occuring from the Upper Oligocene onwards. The earliest known western hemisphere occur- rences of Mytilopsis appear to be the records from the Oligocene of Panama and western Peru discussed below. The fossil record, thus reinterpreted, suggests that both Congeria and Dreissena might be derived from Mytilopsis, rather than that Mytilopsis is descended in some way from Dreissena as has been previously held (Morton 1970). A further consequence of this revision of the fossil history of Mytilopsis is that the numerous cases of its suspected introduction to new areas now need re-examination. As long. Fig. 320 Western Hemisphere Neogene distribution of Mytilopsis. as it was acce
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