THE REV. PETER BELLINGER BRODIE, in his “History of the Fossil Insects of the Secondary Rocks of England,” gave a figure of a small fly which he named Culex (?) fossilis. This insect, from the Purbeck strata, would be by far the oldest mosquito known, were it a veritable Culex. Unfortunately, it is impossible to form any definite opinion, and as positive evidence of the antiquity of the Culicidae the specimen must be dismissed as valueless. On general grounds it is very improbable that the group is so ancient. In Handlirsch's great work on fossil insects several Culicidae are listed from the Oligocene Tertiary; but Handlirsch did not know that two species described by Scudder, from Wyoming and Utah respectively, are actually much older, coming from Eocene rocks. The one from Utah is of little value, and presumably not a true Culex; but that from the Green River beds of Wyoming has the unmistakable features of a genuine mosquito, showing the long proboscis and the short palpi of the female. According to Schuchert's estimates of geologic time, this should be more than two million years old at the very least. Scudder's insect, called Culex damnatorum is 6 mm. long, with a proboscis 1.9 mm. It doubtless tormented the Eohippus and related mammals of this general period. Whether it carried any pathogenic protozoa we can, of course, never know. It is now possible to put on record a second Eocene mosquito, found by Mr. Dean E. Winchester, of the U.S. Geological Survey, at Smith's Ranch, in the vicinity of the Cathedral Bluffs, in western Colorado. It is represented by a female, preserved in lateral view, 5.2 mm. long, the wing about 4.2 mm., thorax about 2 mm., palpi about 0.4 mm., and the distinctly curved proboscis 3 mm. The stout abdomen is like that of true Culex, obtuse at the end, not tapering as in Aedes. The longer proboscis readily separates it from Scudder's insect, so it must stand as a new species, to be called Culex winchesteri, after its discoverer. The horizon is considered to be Green River, approximately equivalent to that of the Wyoming locality.