Eocene cetaceans from the Helmstedt region, Germany, with some remarks on Platyosphys, Basilotritus and Pachycetus

New archaeocete remains from the Helmstedt region, Germany, are reported. The first series of bones is from the open cast mine at Alversdorf, 2 km to the northwest of Offleben, consisting of isolated vertebral centra, rib fragments and two teeth. The second series of bones, a skull fragment, an unidentifiable, triangular bone, vertebrae and rib fragments, as well as a distal tibia fragment, has been found in the open cast mine Treue, about 5 km to the northeast of Schöningen. Historically, from the same Helmstedt region, cetacean vertebrae and rib fragments have been described by Van Beneden in 1883 (and also published by Geinitz, 1883b). He regarded the remains as belonging to mysticetes from the Oligocene, for which he erected the genus Pachycetus. Here, Pachycetus robustus Van Beneden, 1883 is assigned as type species. Vertebra NsT90 is herein assigned as lectotype for that species. Kuhn (1935) ascribed these fossils to archaeocetes and added some newly found vertebrae in his description. Lienau (1984) figured additional cetacean remains from the same region. Presumably all these finds (the older as well as the new material here reported for the first time) have been derived from marine beds of the Gehlberg Formation, which is Bartonian to Priabonian in age. At least two taxa are recognised: a large one (consistent with Pachycetus Van Beneden, 1883), and a smaller one (consistent with a small ‘dorudontine’). A comparison is made between the new material and the earlier described finds, as well as with archaeocete fossils from eastern Europe (Ukraine and southwestern Russia). Some notes are added on the validity of the genus names Platyosphys Kellogg, 1936 and Basilotritus Gol’din & Zvonok, 2013, which are here referred to as Pachycetus.