140 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY, 
by means of an imaginary Antarctic continent, must be relegated on 
both biological and geological evidence to the same category as the 
Lemurian hypothesis. 
Rhea still enjoys a comparatively wide distribution in South America, 
and its remains have been found in the bone caverns of Brazil. If the 
evidence of Diatryma in New Mexico means anything at all, it would 
point to a connection between a fossil North American and the existing 
South American ostrich. It is true that the late Tertiary yields no 
evidence of Struthious birds in North America. But it is also true that 
until the discovery of Struthiolithus under the shadow of the Great Wall 
in China, no one could have suspected the whole intervening territory 
between Northeastern Asia, South Russia, and Africa to have been in 
comparatively recent times inhabited by true ostriches. The palæonto- 
logical record is from the nature of things very deficient in the case of 
land birds, and many gaps,can only be filled on indirect evidence. One 
such gap is now partially filled by the occurrence of Struthiolithus in 
Northern China. A race having the constitutional vigor and numerical 
force to establish itself in this latitude, — and in a mountainons region 
as well, where the struggle for existence is always intensified by a larger 
number of enemies than are found on the plains, to say nothing of the 
rigors of winter, — must have been able to penetrate still further north- 
ward, and might readily have accompanied the mammals that migrated 
across the land bridge formerly connecting the palænretie and nearctic 
regions. 
In a word, if we can predicate any blood relationship between the 
African and South American ostriches, it is certain that the latter could 
have reached its present habitat in no other way than along the route 
marked by Struthio camelus, S. karatheodoris and S. asiaticus, Struthio- 
lithus, Diatryma, and the Rhea of Brazilian bone caverns. If any will 
presume to deny a relationship between Struthio and Rhea, they are 
confronted with these difficulties: to explain how two separate deriva- 
tives from Carinato birds should come to present such marvellous 
similarity to one another through the operation of purely fortuitous 
conditions, and to point out a lineage for Rhea connecting it more 
closely with Carinates than with the ancestors of Struthio. Sceptically 
inclined individuals are welcome to regard Rhea as one of the “waifs 
and strays of a lost avifauna left by the sea of time stranded on the 
shores of the present,” but we personally prefer the more positive 
view, which connects the New and Old World ostriches in the manner 
indicated. 
