72 18 October 1979 PROC. BIOL. SOC. WASH. 92(3), 1979, pp. 494-497 AN OLD WORLD OCCURRENCE OF THE EOCENE AVIAN FAMILY PRIMOBUCCONIDAE Storrs L. Olson and Alan Feduccia Abstract.—Parvicuculus minor Harrison and Walker, from the Lower Eocene of England was incorrectly assigned to the Cuculidae (Cuculiformes) by its authors and is here referred to the Primobucconidae, a family hitherto known only from the Lower and Middle Eocene of Wyoming. Procuculus minutus Harrison and Walker, also from the Lower Eocene of England, belongs neither in the Cuculidae, among which it was originally placed, nor in the Primobucconidae; its affinities are at present considered uncertain. Primoscens minutus Harrison and Walker, described in a new Lower Eocene family, Primoscenidae, of Passeriformes, is not a passeriform, but its true affinities are likewise unclear. The presence of the Primobucconidae in the Lower Eocene of England and Wyoming lends support to other evi- dence for a land corridor across the North Atlantic in the early Eocene and further confirms the idea that the small arboreal birds of the Paleogene in the northern hemisphere were non-passerines. The predominant group of small, arboreal birds recorded from the Eocene of North America is the family Primobucconidae, of which two genera and four species are known from the Lower Eocene of Wyoming, and four species in three additional genera from the Middle Eocene, also in Wyoming (Feduccia and Martin, 1976). These birds are apparently most closely related to the modern Bucconidae, which is currently placed in the Piciformes, al- though more probably the Bucconidae, along with the Galbulidae, belong with Coraciiformes (Sibley and Ahlquist, 1972; Burton, 1977; pers. observ.). In a recent study of a Lower Eocene avifauna from England, Harrison and Walker (1977) named a new genus and species of cuckoo (Cuculiformes, Cuculidae), Parvicuculus minor, based on a tarsometatarsus lacking the inner trochlea. Their description and illustrations are sufficient to indicate that this specimen is clearly referable to the Primobucconidae and has no affinity with the Cuculidae. There is precedent for such an error in that the primobucconid Uintornis lucaris Marsh had been referred to the Cuculi- formes (Cracraft and Morony, 1969) until the manifest differences between these two groups were detailed by Feduccia and Martin (1976). We have compared Harrison and Walker's illustrations and descriptions of Parvicuculus minor with the characters listed in the diagnosis of the Primobucconidae (Feduccia and Martin, 1976:103-104) that are determinable