In a notice published on page 160 of the present volume it was suggested that Arsinoitherium, of which a brief description was there given, must be placed in the order Amblypoda, constituting a new family, the Arsinoitheriidæ. Having further considered the evidence available, and having, moreover, had the advantage of some discussion on the subject with Professors H. F. Osborn and W. B. Scott, I have now come to the conclusion that Arsinoitherium differs from the Amblypoda in so many points that it seems necessary to refer that remarkable mammal to a new subdivision of the Ungulata of equal value with the Amblypoda and Probosoidea, to both of which a certain degree of relationship may exist. For this new order the name Barypoda is proposed, in allusion to the massive character of the limbs in the species at present known. The existence of two orders so marked as the Proboscidea and the Hyracoidea in the Eocene beds of Egypt, and their absence at that period from the rest of the world (with the possible exception of South America), at least make it seem likely that in an area so isolated there were other equally distinct groups which died out before circumstances became favoui'able to allowing them to pass over to other regions. That Arsinoitherium may be the representative of such an order is probable, for its great size and highly specialised character point to its being the closing member of a long line, of which the earlier forms are at present quite unknown, and must be sought in earlier horizons in the Ethiopian region.