472 The American Naturalist. [May, 
quate explanation in my late memoir in Zhe American Journal of 
Morphology.8 This was based on the fact already recorded by Allen 
in his analysis of the Muybridge photographs, that in recover the 
weight is borne on the inner edge of the foot, and therefore on the 
external sides of the heads of the metapodials, I did not then state 
with sufficient clearness what I now add, that the external torsion of 
the lower leg concerned in producing diplarthry is that which occurs, as 
I have pointed out, at recover, and it is therefore coincident in time 
with the transfer of the weight to the inner side of the foot, so that 
both strains occur togéther, and so dislocation cannot occur. In 
rapid movement, when the torsion-strain is most energetic, all the 
strains will be nearly contemporaneous ; while in slow movements the 
torsion on plantation will be distinct, if existing, of which there is | 
some doubt. Thus is directed and located the growth-energy, to which 
Prof. Osborn appeals as a sufficient explanation of the phenomenon 
of diplarthry. 
The authors in a few instances, through some oversight, have mis- 
stated the opinions of the present reviewer. Thus Prof. Scott cites 
him as having regarded the genera Amynodon and Metamynodon as 
identical. This he has not done, as can be seen by his systematic de- 
scriptions of the two genera in ‘‘ The Perissodactyla,’’ (NATURALIST, 
1887, P. 993). Prof. Osborn quotes my earlier Acie of Deis 2 
that Triplopus is in the phylum of the rhinoceroses, ts to 
mention the modified view expressed in ‘‘ The nis F T. 
that it is in the line of Hyracodon, and at one side of the rhinoceroses. 
The slender legs of the known species of this genus are, however, not 
to be regarded as a generic character, as is done by Osborn, and a 
‘stout-legged Triplopus is by no means an impossibility, Finally, 
Osborn accuses me of regarding carpal and tarsal displacement as 
having preceded in time digital reduction, because I stated that one 
consequence of displacement had been the loss of the inner digit. This 
accusation is quite inexcusable, as I have never thought it necessary to 
express any opinion on the subject. Phenacodus (with which I am 
somewhat familiar) shows that reduction preceded displacement, to 
say nothing of Hyrax, cited by Osborn. Reduction f:llowed disuse, 
and it is only the inner digit that has suffered finally through displace- 
ment.—E. D. Cope. 
Note on the Pelvis of Cumnoria (Camptosaurus),—In a 
recent examination of Mr. Lydekker’s admirable volume on vertebrate 
paleontology, I was struck with the conspicuous perpetuation of an 
* On the Mechanical Origin of the Hard Parts of the Mammalia, 1889, p. 171. 
