458 H. G. SEELEY ON A MAMMALIAN FEMUR AND 
and the articular head directed less upward and more inward. In 
all these points of difference there is a nearer approach to the femur 
of Echidna, which, however, is twice as long. In that genus the tro- 
chauters are relatively less developed, and the head of the bone is 
less well defined on the inferior aspect, while in the fossil the in- 
ternal trochanter has a greater proximal extension. Both these 
genera of living Monotremes agree in possessing a similarly unex- 
cavated condition of the posterior aspect of the external trochanter ; 
and there are enough intermediate steps between the two surviving 
genera to include such a form as this fossil bone, if there were any 
corroborative evidence to justify its location in the same order with 
them. 
Among the marsupials there are not many in which a sufficiently 
near correspondence can be detected to justify a comparison. It is 
only among some of the Phalangers, such as Phalangista Cookit, 
that there is a general resemblance seen in form and type, though 
the existence in that group of an obturator pit renders detailed com- 
parison impossible. The only other marsupial to which reference 
may naturally be made is the Myrmecobius, interesting from its 
resemblance to Amphitherwwm ; but the bone is relatively shorter than 
in Myrmecobius fasciatus ; the condyles at the distal end are re- 
latively much less thickened. ‘The internal trochanter does not ex- 
tend so far proximally in the recent genus, and the fossil shows no 
trace of the excavation of the inferior aspect of the proximal end. 
It may therefore be concluded that the resemblance to Marsupials 
is, on the whole, less evident than the probable affinity of the bone 
to a Monotreme. It is interesting that Amphitherium has presented 
characters in the inflected angle of the lower jaw which induces 
Prof. Owen to dwell on its resemblance to the mole and the hedge- 
hog, and to express a necessary caution against hastily concluding 
that the animal was not insectivorous. Dr. Gill, one of the most 
profound systematists of modern times, has sufficiently recognized, in 
his tabular view of the classification of the Mammalia, the near 
affinity of the Chiroptera, Insectivora, Rodents, and Edentates with 
the Marsupial and Monotreme orders ; and it is certainly remarkable 
that this fossil bone, like the jaw referred to, should present cha- 
racters which necessitate close examination as to its placental or its 
implacental determination. There are many animals in which the 
proximal end of the femur has two well-developed trochanters, and 
from which the obturator pit is absent; but in none do the condyles 
attain so great a size as in the fossil. 
In the Little Ant-eater (Cyclothurus didactylus) the femur is 1,3, 
inch long, while the transverse measurement across the trochanters 
is only ,!, inch, so that in this animal the shaft is 37 times as long 
as the transverse measurement over the trochanters, while in the 
fossil the shaft is not more than twice as long as the width over the 
trochanters. The femur of the Mole has only a general resemblance 
to the fossil; the trochanters are narrower; the great trochanter is 
more developed proximally, and the concave area between the tro- 
chanters is of an altogether different character. A similar remark 
