i 
HUMERUS FROM THE STONESFIELD SLATE. 457 
extension beyond the proximal articulation is hardly more than 5 
inch. It is in no sense a process, but simply an expansion of the 
bone, and terminates distally in a short sharp ridge on the angle of 
the side of the shaft. The external trochanter is much thicker, and 
extends beyond the border of the articular head for 72; inch. It is 
separated from this convex surface by a concave excavation about 
jg inch wide; and its outer rounded border, which is nearly ;4, inch 
thick, is reflected backward, and terminated proximally in a rounded 
process, which at the proximal end curves a little forward. 
The rounded articular head has no neck connecting it with the 
shaft; but a constriction extends below the globular surface pos- 
teriorly, and another depression is apparently more marked on the 
anterior aspect. ‘The transverse measurement of the head is about 
=; inch, and the antero-posterior measurement is somewhat more. 
lts depth on the posterior aspect is about ;°, inch. 
Between the head of the bone and the two trochanters is a con- 
cave space, which runs down the shaft for about one third of its length, 
disappearing in a line as the bone narrows from side to side, and it is 
deepest towards the great trochanter. There is no trace of an ob- 
turator pit, nor of any excavation towards the external trochanter, 
such as characterizes this part of the bone in the majority of mam- 
mals, and especially marsupials; so that at first sight there is a 
prima facie suggestion in this region of bats, or moles, or of a type 
allied to the monotremes, in which the trochanters were less deve- 
_ loped than in Ornithorhynchus ; but there are slight concavely curved 
lines extending between the trochanters and indicating muscular 
attachment. 
The shaft becomes reduced to its least width of about 3, inch 
near the middle. Its posterior lateral outline is concave, so as to 
give the distal articulation the aspect of being produced slightly 
outward. The internal outline is nearly straight between the in- 
ternal trochanter and the distal articulation. The shaft of the bone 
is evidently flattened naturally, is straight on the posterior aspect 
below the trochanters, and becomes convexly curved from side to 
side. There is a slight groove extending down the length of 
the shaft in the median line from the external trochanteroid ridge 
to between the condyles, and gradually widening distally. The 
width of the bone across the distal condyles is rather less than 5%; 
inch; and though the specimen is not sufficiently developed from the 
matrix to show the thickness of the condylar end, it was evidenily 
much less thick than is usual among marsupial mammals. The 
outer condyle is the larger; it has a transversely ovate outline, and 
is divided on the posterior aspect by a moderately deep depression 
from the smaller inner condyle, in which the greatest measurement 
was vertical. The depth of these condyles is about 51, inch, and . 
the shaft above them is concavely excavated. 
These are the characters on which the systematic position of the 
animal must be determined. The bone is altogether less robust and 
is rather smaller than the same bone in Ornithorhynchus, has the 
trochanters narrower and smaller, the distal condyles narrower, 
