1912 | Miller: Pacific Coast Avian Palaeontology 101 
groups as the Struthiones and the Stereornithes are in question, 
it would seem that the chief ‘value of Cope’s discovery is to 
show us that a group of gigantic terrestrial birds can inhabit 
a region and leave almost no trace of their oceupation of that 
part of the globe. The same fact is pointed out by Eastman*® 
in his discussion of Struthiolithus and the distribution of the 
Dromaeognathae. Before the discovery of this species in the 
superficial deposits in the mountainous regions of northern 
China no one would have surmised that this great area to the 
north of India was ever inhabited by struthious birds. Why not 
expect, then, with perfect propriety, that some day the path of 
immigration of Rhea into South America may be traced in yet 
undiscovered deposits of North America ? 
The other principle which encouraged the search for rheaids 
in the asphalt, that of a northward migration of southern forms 
in the Pleistocene, is applicable whether Rhea be considered a 
product of the southern continent or not. Among mammals we 
have the northward diffusion of the various edentates and 
Hydrochoerus, which may be considered products of southern 
soil, and we have also a re-entrance from the south of certain 
forms which are Neogaeic by adoption. For example, we may 
look upon Didelphys as having performed such migration. The 
objection might be raised that the tropical belt would act as a 
barrier preventing the plains-dwelling Rhea from retracing its 
steps, but such an objection is reduced to questionable validity 
by the presence of true rheids in the cavern deposits of Brazil. 
The following is a list of lipotypes which are considered by 
the author as of particular interest: 
List or LirpoTyPEs 

Gavia, sp. Palamedeidae—all species 
Gyparchus papa Auct. Cariamidae—all forms 
Thrasaétus harpya Auet. Phororhacidae—all species 
Polyborus cheriway (Jaquin) Gaura, sp. 
Cracidae—all species Plegadis, sp. 
Columbae—all species Ajaia, sp. 
Psittaci—all species Geocoeeyx californianus (Lesson) 
36 Eastman, C. R., Bull. Mus. Comp. Zool. Harvard Coll., vol. 32, p. 
127-144, 1898. 
