P.  Goeldlin de Tiefenau, Maibach, A., and Speight, M. C. D., ?Sur quelques especes de Platycheirus  (Diptera,  Syrphidae)  nouvelles  ou  meconnues. ?, Dipterists Dig. (Ist Ser.), vol. 5, pp. 19-44, 1990.

M. C. D.  Speight and Goeldlin de Tiefenau, P., ?Keys to distinguish Platycheirus angustipes, P. europaeus, P. occultus and P. ramsarensis  (Dipt.,  Syrphidae) from other clypeatus group species known in Europe?, Dipterists Dig. (Ist Ser.), no. 5, pp. 5-18, 1990.

A.  Wright, ?British Sawflies (Hymenoptera: Symphyta) a key to the adults of the genera occurring in Britain?, Field Studies, vol. 7, no. 3, pp. 531-593, 1990.

D. M.  Cohen, Inada, T., Iwamoto, T., and Scialabba, N., ?FAO Species Catalogue. Vol. 10. Gadiform fishes of the world (Order Gadiformes). An annotated and illustrated catalogue of cods, hakes, grenadiers and other gadiform fishes known to date?, 1990.