AMPHITHERIUM. 53 
exceed the number usually found in the unguiculate Mam- 
malia. The marsupial genus, Myrmecobius, (fig. 18,) has 
nine molars on each side of the lower jaw, besides one small 
canine and three conical incisors. 
Nat. size. 
MYRMECOBIUS FASCIATUS, 
The teeth of Amphitherium, moreover, differ from those 
of Didelphys not only in number but also in size, being 
relatively smaller. The teeth of M/yrmecobius, besides their 
approximation im number to those of Amphitherium, re- 
semble them in their small relative size more than do those 
of Didelphys, but they are still smaller than in Aimphithe- 
rium, which in this respect, as well as in the structure of 
the teeth, appears to hold an intermediate position between 
Didelphys and Myrmecobius. The incisors (7) of the 
Myrmecobius are conical, separated at their base, diverging, 
the anterior one almost as long as the canine (/) ; the first 
three molars (p) have compressed, conical, bicuspid, or 
tricuspid, crowns, the middle cusp being the largest, and 
they have each two fangs; they belong to the series of 
premolars: the remaining six teeth are multicuspid and 
true molars, as in Amphitherium. 
The discovery of an existing quadruped in the marsupial 
series, presenting so many resemblances in the number, 
size, shape, and proportions of the teeth, to the Amphithe- 
rium, so far as the dental characters of that genus are 
elucidated by the two specimens above described, adds to 
