HUMERUS FROM THE STONESFIELD SLATE. 461 
difference of the bone from the same element in Ornithorhynchus, it 
should be borne in mind that the Monotremes are at present known 
to us very imperfectly, and that between the Duck-billed Platypus 
and the Echidna there is a wide interval of organization. But per- 
haps the most interesting evidence of the affinity of the humerus is 
obtained when we bear in mind that it is found with the femur, 
and that the two bones correspond in presenting predominant indi- 
cations of Monotreme characters under the external forms usual 
among Marsupials. 
The only history of these specimens is that they were collected by 
Mr. 8. Peace Pratt, formerly one of the Secretaries of the Geological 
Society, and presented by him, with four other bones from Stonesfield, 
to the British Museum. Mammalian remains occur so rarely that there 
is a strong predisposition to regard these bonesas naturally associated ; 
and the somewhat smaller size of the humerus, as compared with 
the femur, would favour such judgment, however strong the temp- 
tation might be to refer the bones to different genera on account of 
their resemblances to such different types of existing animals. At 
least, in the absence of evidence to the contrary, it may not be in- 
convenient to consider them to have been portions of a single indivi- 
dual. There then arises the more difficult question as to whether they 
pertain to any of the genera of the Stonesfield-Slate mammals hitherto 
established or not. And necessarily a judgment on this point must 
be largely founded on probabilities. ‘The comparatively large Ste- 
reognathus is so generally regarded as placental, that its claims to 
the humerus and femur may be dismissed. There then remain 
only Amphitheriwm and Phascolotheriwn with which they may be 
associated. The size of the bones is not very different from what 
might be anticipated from the length of the jaws already described 
in those genera. In many small animals the length of the lower 
jaw is not greatly different from that of the femur, and the humerus 
is usually somewhat shorter, though there are many animals in which 
the skull is much longer than the femur. In Ornithorhynchus the 
lower jaw measures 34 inches, the femur 1,4, inch, the humerus 
1,3; inch. In Echidna the skull is 4;4, inches long, the femur 2,5, 
inches, the humerus 1,8, inch. In Didelphis virginiana the lower 
jaw is 3,5, inches, femur 3,1, inches, humerus 2,9; inches. In Myr- 
mecobius fasciatus the lower jaw is 1,8, inch, femur 1,%, inch, hu- 
merus 1,4, inch. In Phalangista Oookw the lower jaw is 1,5, inch, 
the femur 2,7, inches, the humerus 24, inches. In Phascolarctos 
the lower jaw is 2,5, inches, femur 3,5, inches, humerus 2%; inches. 
In the Little Ant-eater the lower jaw 1s 1,2, inch, the femur 1,°, inch, 
the humerus ;% inch. In the Hedgehog the lower jaw is 1,5 inch, 
and the femur and humerus are of the same length. In the Mole 
the skull is 1,4, inch, femur 54 inch, and humerus ;°, inch. In the 
Beayer the lower jaw is 2,3, inches, femur 2, inches, humerus 1,9, 
inch. In the Marmot the lower jaw is 2,%, inches, the femur 3 
inches, the humerus 2-5, inches. 
Now in Phascolotherium the length of the jaw is about 1,4, inch, 
and in Amphitherium the length of the jaw is about 1, inch, while 
