on Dr. Harlan’s New Fossil Mammalia. 209 
Prof. Owen pronounces me in error in supposing that his genus 
“ Mylodon,” is founded on my genus Megalonyr laqueatus ; the 
latter he admits is a true Megalonyx, and by no means to be in- 
cluded in his Mylodon. My original description of M. laquea- 
tus, was published in the Philadelphia Journal of the Academy 
of Natural Sciences in 1831. Subsequently, perhaps about the 
close of the same year, I published in the “‘ American Monthly 
Journal of Geology,” ‘a description of the jaws, teeth, clavicle, 
&c. of the Megalonyx laqueatus’’—fossils then in the collection 
of Mr. Graves of New York. 
Now, the “error” above noticed, rests entirely on a difference 
in opinion between Dr. O. and myself respecting the true nature of 
these New York specimens. Ona careful inspection at the time, 
I considered them as belonging certainly to the genus Megalonyz, 
and as closely allied to if not identical with the JZ. laqueatus. 
But when the entire skeletons of individual species cannot be 
examined, it is not easy to pronounce with certainty in all cases, 
on the identity of species. Dr. O. relies in every instance on the 
structure, arrangement, &c. of the teeth, in his designation of 
species, without conceding to other portions of the skeleton a 
relative importance. 'T'o me it appears that the organs of masti- 
cation, viewed alone, are more liable to lead to error in forming 
distinctive characters than are the organs of locomotion; thus, 
in form, structure, and arrangement of the enamel, the superior 
molars of the horse differ more from the inferior molars of the 
same individual than do the molars of the Megalonyz of the 
New York specimens from the M. laqueatus of my original me- 
moir. 
On a careful examination and comparison of the tibiee in both 
specimens of Megalonyzr, I could perceive no specific difference, 
much less discrepancies authorizing the adoption of a new genus 
for it, as Dr. O. has done under the name of Mylodon. 'The 
form and structure of the tibia in my new genus “ Orycterothe- 
rium” of Missouri is totally distinct from either. Professor Owen 
has founded his observations of the characters of the New York 
species on the drawings of the cast of the jaws and teeth, to- 
gether with the figures accompanying my memoir. In the pres- 
ent state of our inquiries, I think that we are not yet prepared to 
pronounce with certainty that “the name Orycterothertum Mis- 
souriense, must sink into a synonym of Mylodon Harlani.” 
Vol. xiv, No. 1.—April-June, 1843. 27 
