The genera Muellerina Bassiouni, 1965 and Thaerocythere Hazel, 1967 from the Neogene of Northwest Europe

Abstract. Twenty one species of the genera Muellerina and Thaerocythere are considered. Of these, 11 species, including the type species of both genera, have been described previously. Two species are left in open nomenclature due to inadequate numbers but eight are described as new. These species are: Muellerina latimarginata (Speyer, 1863), M. abyssicola (Sars, 1866), M. lacunosa (Jones, 1857), M. praeabyssicola Uffenorde, 1981, M. parvipunctata Uffenorde, 1981, Thaerocythere crenulata (Sars, 1866), T. hoptonensis (Brady, Crosskey & Robertson, 1874), T. mayburyae Cronin, 1991, T. oedichilus (Brady, 1878), T. trachypora (Jones, 1857), T. trapezia (Brady, 1878), and the new species M. dolabrata, M. metabyssicola, M. orygyma, M. pliocenica, T. biformis, T. praecrenulata, T. vermiculata, T. woutersi and T. wittei. The phyletic relationships of these northwestern European species are considered.