The typical Genus _Culex_ contains 21 species scattered all over Australia; several are cosmopolitan and have been introduced from abroad. Our common house mosquito, that appears in the early summer, is _Culex albo-annulatus_, a moderate sized species with the reddish thorax densely clothed with brownish golden scales, traversed by five very fine lines; it has regularly white banded legs. It was described by Macquart in 1732, and ranges from Southern Queensland to Sydney, Mittagong, and the Blue Mountains N.S.W. _Culex fatigans_ is widely distributed over Australia: _C. macleayi_ and _C. skusei_ according to Theobald are only sub-species or varieties; it is one of the cosmopolitan mosquitoes also found in America, Africa and Asia, and was probably introduced into this country in the water tanks of the old sailing vessels many years ago. After New Year a smaller, darker mosquito is the most annoying about Sydney; this has been described by Theobald under the name of _Culex marinus_; its larvae were discovered by Dr. Bancroft, Queensland, breeding in salt water. It also flourishes freely in any stagnant water left in tanks, buckets, or water-holes, and has a wide range down our eastern coast. Four species of the Genus _Anopheles_ are found in Australia; these insects have long palpi with clubbed or spatulate tips, and dark spotted wings. _Anopheles annulipes_, described by Walker, said to be identical with Skuse’s _A. musivus_, is found about Sydney and Newcastle N.S.W. ranging northward; the members of this genus are well known as the mosquitoes that transmit the germs of malarial fever, and have a wide range over the world. The important results that have come from the study of the relation of tropical fevers to mosquito bites, have led to the collection and description of these insects from all quarters of the globe. _Mucidus alternans_, one of our largest species, is thickly clothed with grey and light brown scales and hairs which give it a striking appearance. It is a day flying species famous for its biting powers; it has a wide range; in the Maitland district N.S.W. about the Hexham swamps it is locally known as the “Hexham Grey”; in Queensland it is sometimes called the “Scotch Grey.” I have also taken it at Bourke on the Darling River N.S.W. Skuse described this species as _Culex hispidosus_, but Westwood’s name, _C. alternans_, has a prior claim. _Stegomyia notoscriptus_ is one of the small dark mosquitoes that bite so sharply just at dusk in our gardens around Sydney in midsummer, and has a wide range from Adelaide S.A. to Queensland. It belongs to the same genus as the dreaded Cuban Yellow-fever Mosquito, _Stegomyia fasciata_, which has been introduced into Hawaii. Theobald has in the last volume of his Monograph formed a new Genus _Skusea_ for the reception of two Queensland species and a third from Africa. Family 4. Sand-flies. CHIRONOMIDAE.