SCIENTIFIC SUMMARY. 
179 ' 
of ribs, a sternal bone, a scapula, and a right humerus, found imbedded in 
one mass of rock, and of a femur and phalanges, and a pelvis in another 
mass. With the exception of the pelvis, Prof. Owen described these bones 
in detail. The vertebrae agree most nearly with those of Dicynodon , and 
Oudenodon. The supposed sternal bone is of a rounded hexagonal form, and 
is regarded by Prof. Owen as the anterior bone of the sternum proper, which 
is usually unossified in recent lizards, but well ossified in Ornithorhynchus. 
The scapula also presents resemblances to that bone in Ornithorhynchus. 
The humerus in its general proportions, and especially in the great develop- 
ment of its ridges, was also shown to> resemble the same bone in the Mono- 
tremes. The ungual phalanges were described as broad and obtuse, probably 
constructed to bear claws adapted' for- digging, as in Echidna; the femur also 
resembles that of the last-named animal. 
Prof. Owen remarked upon these approximations to the Monotrematous 
Mammalia, in allusion to which he proposed the name of Platypodosaurus 
robustm for this animal, the humerus of which was 10| inches long and 
nearly 6 inches broad at the distal end. He also alluded to the interesting 
problems- opened up by the study of these South- African reptiles in connexion 
with their possible relationships to the low implacental’ Mammalia of New 
Guinea, Australia, and Tasmania. 
Subsequently the pelvis was freed from-, the -matrix, and Prof. Owen com- 
municated a description of this part of the skeleton to the Geological 
Society (9th March, 1881). The fossil includes the sacrum, the right ‘ os 
innominatum/ and a great part of the left ilium. There are five sacral ver- 
tebrae) which Prof. Owen believes to be the total number in Platypodosaurus. 
The neural canal of the last lumbar vertebra is eight lines in diameter, and 
of the first sacral nine lines, diminishing to six lines in the fifth, and indi- 
cating an expansion of the myelon in the sacral region, which is in accordance 
with the great development of the hind limbs. The sacral vertebrae in- 
crease in width to the third; the fourth has the widest centrum. The 
coalescence of the vertebrae justifies the consideration of the mass, as in 
Mammalia, as one bone or 1 sacrum/ which may be regarded as approaching 
in shape that of the Megatherioid Mammals, although including fewer ver- 
tebrae. Its length is 7\ inches ; its greatest breadth, at the third vertebra, 
inches. The ilium forms the anterior and dorsal wall's- of the acetabulum, 
the posterior and postero-ventral walls of which are formed by the ischium 
and pubis. The diameter of its outlet is 3 inches,, the depth of the cavity 
1| inch, and at its bottom is a fossa inch broad.. The foramen is sub- 
circular, 1 inch in diameter. The ventral wall of the pelvic outlet is chiefly 
formed by the pubis,; it is a plate of bone 6 inches broad,, concave externally, 
convex towards the pelvic cavity. The subacetabular border is 7-8 lines 
thick ; it shows no indication of a pectineal process, or of a prominence for 
the support of a marsupial bone. Prof. Owen remarks that of all examples 
of pelvic structure in extinct Reptilia this departs furthest from any modi- 
fication known in existing types, and makes the nearest approach to the 
Mammalian pelvis. This is shown especially by the number of sacral ver- 
tebrae and their breadth, by the breadth of the iliac bones, and by the extent 
of confluence of the expanded ischia and pubes. 
At the same meeting Prof. Owen described another new South African 
