THE AMERICAN NATURALIST. [Vol. XXXVII. 



lithographica and its allies. Gill, Stejneger, and others have 

 used the term Eurhipidurae for all birds in contradistinction 

 to the Saururae, while the last-named author throws the 

 toothed birds of the American Middle Cretaceous outside of it. 

 Now as Eurhipidurae means "fan-tailed birds," it is a term not 

 strictly applicable, for neither the struthious birds nor the grebes 

 possess fan tails, while it is more than likely that the represen- 

 tatives of the ichthyonine birds did, and this very probably 

 was the case too with Hesperornis. As with so much that 

 now goes in avian taxonomy, even the lizard-tailed (Saururae) 

 and the bird-tailed (Ornithurae) orders can only be considered 

 provisional divisions. However, they can do duty until the 

 day comes when a fossil bird is discovered somewhat more rep- 

 tile-like than Ichthyornis, but presenting in the skeleton of its 

 tail a decided advance birdwards from Archaeopteryx, even to 

 the point of the first stages of the formation of a pygostyle. 



SUPERSUBORDER DROMvEOGNATHiE. 



In this group it is intended to include all the existing and 

 extinct struthionine birds which are morphologically closely 

 allied to the ostrich (Struthio camelus). This will include the 

 Dinornithidae, but obviously exclude the Apterygidae, the Cryp- 

 turidae, and other families that are not ostriches in any sense of 

 the word, any more than was the American cretaceous toothed 

 loon, the Hesperornis. It comes about as near the expression 

 of true avian affinities to associate the tinamous with the 

 ostriches, for the reason that the posterior extremities of their 

 ilia and ischia have remained free, as it would be to relegate 

 the cassowaries to the crane group, simply because in them 

 those bones fuse together in the adult. 



The supersuborder Dromaeognathae includes the following sub- 

 orders, namely: (i) Strnthiomithcs ; (2) Rheornithes ; (3) Casna- 

 riornithes; (4) Dinornithes ; (5) ^Epyomithes. 



Of these the Struthiornithes are represented by the existing 

 African ostriches of the family Struthionidae. The Rheornithes 

 include the South American ostriches of the family Rheidas, of 

 which there appear to be at least three well-defined species. 



