The family of Syrphidae is one of the most extensive in the order of Diptera. Nearly or quite two thousand species are known from throughout the world, and many new forms are constantly being added. They contain among them many of the brightest-colored flies, and numerous specimens are sure to appear in every general collection of insects. None are injurious in their habits to man's economy, and many of them are very beneficial. In this work, about three hundard species are described from the region north of Mexico. That there are many more species within these limits is certain, especially in the southern and western regions.