The Ostariophysi are Teleostean Fishes in which the air bladder is connected with the internal ear by a chain of ossicles, the Weberian ossicles, which are modified elements of the anterior vertebrae. Although the order is a large and varied one it is undoubtedly natural, and its importance in Zoogeography arises from the fact that it is dominant in the fresh waters of all parts of the world except Madagascar and the Australian Region. I estimate the number of known species at well over 4,000; of these more than 2,500 are Cyprinoids (Characiniformes 850, Gymnotiformes 30, and the rest Cypriniformes, with nearly 1,500 Cyprinidae) and about 1,600 are Siluroids.