Louis Dollo—On the Humerus of Euclastes. 265 
true Chelone, Since the first Chelonians were certainly terrestrial,’ 
and that the Propleuride are, especially as far as the limbs are 
concerned, nearer to the primitive stock of the Testudinata than the 
living Chelone, it may be inquired whether these Propleuride are 
not the direct ancestors of the latter. I do not think so, for the 
following reasons. Notwithstanding that the Cretaceous beds * con- 
taining Propleuride are, without doubt, older than the Cretaceous 
beds? in which the oldest true Chelone* has been found, and that, 
consequently, in the present state of knowledge, there is no contra- 
diction so far, as to time, I am of opinion that the structure of the 
mandible ® suffices alone to make us consider that descent as impos- 
sible. Indeed, a short symphysis is primitive, a long one derived. 
Therefore, it is not at all likely that the latter has given rise to the 
former. Moreover, the carapace, the plastron, and the choanes ® point 
also in the same direction.’ 
IX.—But, without being the direct ancestors of the Chelonide, the 
Propleuride may enlighten us as to these ancestors, just as Hesperor- 
nis,* which, on account of its much reduced wings, could not be the 
precursor of any of the living Birds, throws light on the dentition 
of the forms from which they have been derived. The Propleuride 
show us the large head,’ the separated nasals,’? and the more 
terrestrial limbs possessed at one time by true Chelone. Thus, 
Paleontology furnishes material proof of facts already foreseen by 
Morphology. 
X.—According to Mr. E. D. Cope," the relations between the 
Dactyloplastrine Cryptodiran Thecophorian Chelonians are the fol- 
lowing : 
Chelydrida. 
Propleurida. 
ia Trionychida. 
I cannot admit this grouping, because : 
1. How could the Trionychide have transmitted to the Propleuride 
the marginal bones, which they have lost themselves ? 
1 G. Baur, ‘‘ Notizen,”’ etc., p. 688. 
2 L. Dollo, “ Euclastes,’ etc. Because, in England, there is no Danian (A. 
Geikie, ‘‘Text-Book of Geology,”’ p. 815) ; and, in the United States of America, 
the fossils found in the Fwclastes-beds, for instance, Teredo tibialis and Gryphea 
vomer, are considered by D’Orbigny as Senonians (Prodrome de Paléontologie strati- 
graphique, Paris, 1850-52). 3 Danian (Tuffeau de Maestricht). 
4°“ Chelone Hoffmanni,’ Gray. . . . ‘ Bis jetzt ist dies indessen das alteste Fossil 
aus Europa, das mit vollem Recht den Namen Chelone tragt’’ (L. Riitimeyer, 
“¢ Ueber den Bau,” ete., p. 119). 
5 L. Dollo, ‘‘ Chéloniens landéniens,” ete., p. 134. 
6 L. Dollo, ‘‘ Chéloniens landéniens,”’ ete., p. 133. 
7 L. Dollo, ‘‘ Euelastes,’’ ete. (loc. cit.). 
8 0. C. Marsh, “ Odontornithes; a Monograph on the Extinct Toothed Birds of 
North America,” New Haven, 1880, p. 62. 
9 L. Rutimeyer, ‘‘ Ueber den Bau,”’ etc., p. 122. 
10 L. Dollo, ‘‘ Chéloniens landéniens,”’ ete., p. 132. 
1K. D. Cope, ‘‘ Tertiary Vertebrata,” etc., p. 115. 
