EASTMAN: REMAINS OF STRUTHIOLITHUS CHERSONENSIS. 135 
determine their precise relations it would be necessary to sacrifice a 
portion of one of the best preserved arcas for the purpose of making 
a thin section; but as no such area is contiguous to the aperture cut 
at the upper end by Mr. Sprague, no further incisions have been at- 
tempted. It is doubtful in any case whether a section would show more 
than has already been ascertained from Nathusius’s study of the type 
specimen, which merely proved that the air canals terminated in a 
similar fashion as in Struthio camelus. But the variations in the struc- 
ture of egg shells among different birds, or even in different parts of the 
same egg, are so considerable,’ that we are averse to depending upon 
this method for accurate systematic identification. In the opinion of 
the writer, the utmost we are warranted in affirming with regard to the 
relationship of Struthiolithus is, that it probably was very like the living 
ostrich, but not necessarily a member of the same genus; hence the 
propriety of retaining Brandt’s name in a tentative sense is apparent. 
The occurrence of fossil ostrich remains in the loess of such widely 
separated regions as Northern China and Russia has a direct bearing 
upon the distribution of Struthious birds. It enables us to speak 
positively with regard to the former extension of the Struthionidæ over 
Eur-Asia and Africa since the Pliocene, and gives rise to some infer- 
ences, within duly circumscribed bounds, regarding the past history of 
Raft-breasted birds in general. It is necessary to distinguish between 
what can be affirmed of the ostrich group, properly speaking, and what 
we can assume with more or less plausibility concerning the rest of the 
so-called Ratite. For, if it were possible to recognize the latter as a 
natural division, embracing forms genetically related to one another, or 
all derived from a common ancestral type (that is to say, a “Ratite ” 
type), then we should be warranted in establishing a single hypothesis of 
distribution for all branches of the Ratite. But the best modern +orni- 
thological opinion holds that the division into Ratite and Carinate is 
unnatural, since the differences between existing species of Raft-breasted 
birds are nearly as great as between any of the Ratite and Carinatæ.? 
1 Blasius, R., Ueber die Bildung, Structur, und systematische Bedeutung der 
Eischale der Vogel. Leipzic, 1867, pp. 48. 
2 Cf. Fürbringer, M., Untersuchungen zur Morphologie und Systematik der 
Vögel, Vol. II. p. 682. Amsterdam, 1888. Also (on the relations of Gastornis) 
under same caption in Biol. Centralblatt, Vol. XIX. pp. 573-587 (1898). On the 
taxonomic relations of Rhea, loc. cit. (1888), p. 1442: of Hesperornis, Ornith. Mo- 
natsber. deutsch. Vereins z. Schutze der Vogelwelt, Vol. XV. p. 488 (1890). 
