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H.  C. Curran, ?Revision of the Pipiza group of the family Syrphidae (Flower-flies) from north of Mexico?, Proceedings of the California Academy of Sciences, vol. 11, pp. 345-393, 1921.

D. W.  Miller, ?Material for a monograph on the Diptera fauna of New Zealand. Part II, family Syrphidae?, Transactions and Proceedings of the Royal Society of New Zealand, vol. 53, pp. 289-333, 1921.

G. H.  Hardy, ?Notes on some Australian Syrphidae (Diptera)?, The Australian Zoologist, vol. 2, pp. 12-18, 1921.

C. L.  Metcalf, ?The genitalia of male Syrphidae, their morphology, with especial reference to its taxonomic significance?, Annals of the Entomological Society of America, vol. 14, pp. 169-225, 1921.