12 On a Group of Extinct Birch from Patagonia. 



The llatitae are in many respects more primitive, and not 

 improbably were already sharply separated from the Carinatse 

 when the Stereornithes arose. 



The absence of specimens of the Stereornithes from Euro- 

 pean museums is much to be regretted, since without actual 

 examination of the bones it is rash to express any definite 

 opinion as to the affinities of the group. Nevertheless, in 

 the meantime it may be suggested that some at least of the 

 Stereornithes may form a specialized offshoot of the stock 

 which gave rise to the Neotropical Gruiformes : possibly 

 some affinities to the Kalliformes may also be found. 



Besides Phororhacos, Ameghino describes several other 

 genera, including Brontornis, Pelecyornis, Liornis, and 

 Callornis, but, in the absence of sufficient material, much 

 less completely. Most likely the number of genera will have 

 to be increased by the retention of some of those founded 

 by Moreno and Mercerat, which have been placed by 

 Ameghino among the synonyms of Phororhacos — e. g., 

 Dryornis, of which the humerus, as figured, is totally unlike 

 that of Phororhacos. Certain of these genera differ so 

 widely one from another that their reference to distinct 

 families seems quite justifiable. Indeed, the Stereornithes 

 seem to be a heterogeneous group of birds in all of which 

 the wings were reduced and the bulk increased through the 

 operation of some peculiar local conditions; for instance, the 

 land which they inhabited may have been an island on which 

 no large carnivorous animals occurred. A similar example 

 is offered by New Zealand, where the Dinornithidse, Apteryx, 

 Aptornis, and Cnemiornis (all flightless birds of large size, 

 belonging to several distinct orders) were formerly found. 

 Indeed, there seems no reason why at any time, from the late 

 Secondary period onward, and in any region, similar groups 

 of flightless birds might not have arisen under favourable 

 circumstances. The Gastornithidse may be another instance 

 of such. In most cases such specialized races die out with- 

 out leaving any descendants when the peculiar conditions to 

 which they have become adapted pass away ; but the modern 

 Ratitai may be survivors of one or several ancient groups of 

 such flightless birds. 



