64 
ORIGINAL ARTICLES. 
Leidy, in the introduction to the “ Fossil Fauna of Nebraska, 
designates the fossil Elephant of North America E. Americanus, as 
distinct from j E. primigenius. But he gives no diagnostic characters, 
and assigns no reason for the change, which appears to be founded 
mainly on the supposed improbability of the same species having 
ranged from Europe to America. His E. imperator , he assumes to 
be distinct, “ because it was found in association in a Fauna very 
distinct from any previously noticed,” (antea, p. 59.) He separates 
the Megatherium of North from that of South America, avowedly on 
these grounds ; and it would appear that he distinguishes his Equus 
fraternus and E . complieatus , from the European forms called 
E. primigenius , and E. plicidens , on the same principled But the 
practice is open to grave objections. It assumes a difference on 
theoretical grounds, where the direct evidence, so far as it goes, indi¬ 
cates the contrary ; and its general adoption would tend to arrest, 
on the threshold, the investigation of the means through which 
remote geographical forms, presenting common characters, may have 
started from a common origin. 
The separation of some of the American Pleistocene Horses and 
Bisons, from the European fossil species, may prove, on the compari¬ 
son of sufficient materials, to be well founded. But as regards the 
true Mammoth, E. primigenius , exclusive of E. Columbi , I am 
satisfied that it rests on no sufficient grounds. The well known 
characters, upon which Cuvier established his definition of the 
species, have been confirmed by the general observation of Palaeon¬ 
tologists up to the present day, namely: the cranium long, with a 
concave forehead, and very elongated tusk-sheaths ; the lower jaw 
rounded, with a rudimentary beak; the molar teeth very broad 
relatively to their lengths, and the constituent layers of ivory, 
enamel, and cement, very thin and condensed. The definition was 
so good, in consequence of its including so many elements of un¬ 
doubted authenticity, presented together in the same individuals. 
But entire skulls are very rare, and it is only under favourable 
circumstances, that entire mandibules are met with ; while the dense, 
hard, and more durable molars occur everywhere. Practically, there¬ 
fore, the identification of the species, in most instances, rests upon 
them : and the characters which they yield are so constant and well 
marked, that with care on the part of the observer, they are per¬ 
fectly reliable, and sufficient for the purpose. In the London 
collections, taking those of the British Museum and College of 
Surgeons together, abundant materials exist for the comparison of 
molars of the American Mammoth with those of the Siberian and 
European forms. The Hunterian collection contains a fine series 
Burlington Kailway, and said to have been from below the Erratic boulder drift* 
which, from recollection he believed to be different from the European Mammoth* 
p. 100. * Op cit. p. 9. 
f Proceed. Acad Nat. Scien. of Philadelphia, 1858, p. 11. 
