ON THE EXTINCT ANIMALS OF NORTH AMERICA. 
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peculiarly American, it might have been expected that when 
the earlier formations of the continent on which they flourished 
were explored, the remains of similar or at least allied forms 
would have been brought to light. But hitherto this has not 
been the case. 
Two species of a genus (. Morotherium , Marsh) allied to 
Megalonyx and Mylodon , from Pliocene strata in Central Cali- 
fornia and Idaho, have been described ; but it is a most remark- 
able fact that not a fragment attributed with certainty to an 
Edentate animal has been found in any Miocene or Eocene 
deposit on the North American continent, and therefore (if this 
negative evidence can be trusted) we shall have to look elsewhere 
(probably to the Southern American continent) for the region 
which gave birth to these mighty creatures, and to look upon 
them as but temporary excursionists into the northern portion of 
the continent during the Pleistocene epoch. 
On the other hand, numerous species of the orders Hodentici , 
Insectivora , and even Chiroptera , and some attributed to the 
Marsupialia , have been found in almost all the hitherto ex- 
plored fossiliferous deposits down to the Eocenes. Of these 
time will not suffice to give an account, and this is less import- 
ant as it is difficult to draw any general conclusions from the 
fragmentary descriptions of them which we possess at present. 
I must, however, not omit to call attention to two recently an- 
nounced discoveries, which, when fully worked out, promise 
results of considerable interest. 
Professor Leidy, in 1868, described a single lower molar tooth 
from a Tertiary formation, supposed to be Miocene, of Shark 
River, Monmouth County, New Jersey, apparently of Ungulate 
affinities, and to which he gave the name of Anchippodus 
riparius. Subsequently a lower jaw of a very anomalous 
character, from the Bridger Eocene, with large rodent-like per- 
petually growing incisors, no canines, and bilobed molars, 
something like those of Palseotherium, was described by the 
same author under the name of Trogosus castoridens ; but 
comparison with the single molar from New Jersey showed so 
close a resemblance, that the latter name was withdrawn, and 
both specimens referred to the first described, or Anchippodus . 
Other similar forms found in a more perfect condition have 
been described by Professor Marsh, who at a meeting of the 
Connecticut Academy, Feb. 17, 1875, suggested that as they 
could be included in no known order of mammals, they should 
be placed in a new one, for which he proposed the name 
; Tillodontia. 
“ These animals,” Professor Marsh observes, w are among the 
most remarkable yet discovered in American strata, and seem to 
combine characters of several distinct groups, viz. Carnivores, 
