The Wallaby Louse Fly, _Olfersia macleayi_, is very common on small marsupials in Australia and Tasmania. When the dogs while hunting pull down and kill a wallaby, these flies generally crawl off and cling to the dog’s nose, rendering him very unhappy. It is a winged form, measuring under ½ an inch to the tip of the folded wings, and is of a uniform shining dark brown tint with a greenish shade very noticeable in the legs. Speiser (Annals Musei Nationalis Hungarici 1904) has placed this species in his Genus _Ortholfersia_. _Ornithomyia perfuga_, taken on an owl (probably _Spiloglaux boobook_) near Brisbane, has been recently described by Dr. Speiser: it is a larger species of a more reddish brown colour. A very fine louse fly, also taken in Southern Queensland upon a white hawk, measures nearly ¾ of an inch to the tip of the folded wings, and has been identified by the same gentleman as _Ornithoctona nigricans_, described originally by Leach. Among the few other species described from Australia is one found on our pretty little emu wren, which was described by Schiner in the “Zoology of the Voyage of the Novara 1850” under the name of _Ornithomyia stipituri_. A number of our native birds act as hosts for these curious flies; the fruit pigeons, swallows, fly-catchers, and others are known to have them; and when they are systematically collected our list will probably be a large one. The NYCTERIBIIDAE are another typical family of louse-flies found upon different bats, which are very small in comparison with the true louse-flies: they are always wingless, and have a world-wide distribution. They are reddish brown creatures covered with stout spines; the head is buried in the thorax; and the legs, very long and slender, terminate in immense pincer-shaped claws. Nearly all our bats are more or less infested with these “spider flies,” and several species have been described. Rainbow has recently described one under the name of _Nycteribia pteropus_ from a flying fox taken at Batavia River, N. Australia (Records Australian Museum 1904). Family 24. Fleas. PULICIDAE. The classification of the fleas has always been a matter of doubt; modern entomologists usually place them at the end of the Diptera, considering them a group of degraded flies that from their parasitic habits have become wingless, and have developed wonderful jumping powers; other specialists who have devoted much attention to the question consider them as worthy to rank in an Order, and follow Latreille, who called them SIPHONAPTERA; other writers, like Taschenberg, who wrote his Monograph entitled “Die Flöhe” in 1880, formed them into distinct families. The latest revision of the family is Baker’s “Revision of American Siphonaptera, &c.” (Smithsonian Institute 1904); in this he gives a list of the described species, placing them in five families, and records a total of 134 species from all parts of the world.