“There is a third family of fishes, the Hornpouts or Bullheads, called Siluroids by naturalists, which seem by their structural character to occupy an intermediate position between the Sturgeons and Goniodonts. There would seem to be, then, in these three groups, so similar in certain features, so distinct in others, the elements of a series. But while their structural relations suggest a common origin, their geographical distribution seems to exclude it. Take, for instance, the Hornpouts; they are very few in the northern hemisphere, hardly ever occurring in those rivers where the Sturgeons abound, and they are very numerous in the southern hemisphere, in southern Asia, Australia, Africa, and South America, where the Sturgeons are altogether wanting. In South America the Siluroids everywhere exist with the Goniodonts, in all other parts of the world without them; the Goniodonts being only found in South America. If these were the ancestors of the Siluroids in South America, they were certainly not their ancestors anywhere else. If the Sturgeons were the ancestors of the Siluroids and of the Goniodonts, it is strange that their progeny should consist of these two families in South America, and in the Old World of the Siluroids only. But if all three had some other common ancestry, it would be still more extraordinary that its progeny should exhibit so specific a distribution upon the surface of our globe. The Siluroids lay very large eggs, and as they are very abundant in South America we shall no doubt have opportunities of collecting them. Of the reproduction of the Goniodonts absolutely nothing is known. Of course the embryology of both these groups would have a direct bearing on the problem of their origin.