RECORDS OF IV. A. MUSEUM. 
[247 
the shaft is situated more distal ly then in the living Echidna, rising 
sharply at a point 20 mm. from the head, from this point a well- 
defined ridge runs to the distal end of the shaft. 
At the longitudinally compressed, and transversely expanded 
distal extremity, the trochlear articular surface is well marked, in 
front it is slightly curved transversely and convex vertically, posteri- 
orly it is divided into two condyles by a wide and deep intercondylar 
notch, which in comparison is deeper and broader than in the 
living Echidna. 
The tibia (plate XXXVII) is straight, laterally expanded at 
the proximal and distal ends with a relatively slender shaft ; the 
anterior convexity of the proximal end of the shaft (the tuberosity 
for the tendons of the extensor muscles) is separated from the 
lateral expansions by two shallow grooves which gradually diminish 
as the shaft becomes more slender, till finally the anterior surface 
becomes a regular convexity. 
At the distal end of the bone and at some distance above it on 
the posterior aspect (plate XXXVII, fig. 3) the concavities and 
convexities for the reception of the bones of the ankle joint and of 
the adjacent fibula are very prominent ; they show no material 
difference in arrangement from the corresponding features in the 
Echidna T. a.ineptus represented in the Museum Collection. 
The fore limb is represented by the right radius only. 
The bone is more slender than the tibia, has its heads much 
expanded laterally ; these are excessively developed in directions 
at right angles to one another. The oval hollow for the 
reception of the humerus is deep with a marked thickening 
at its posterior margin. The distal end has two concavities 
separated by a convex ridge to fit into the convexities of the 
scapholunar, and the small sesamoid bone developed in the tendon 
of the flexor carpi radialis, the concavities are sub-equal, but in 
Tachyglossus aculeatus ineptus, theliving species of Western Australia, 
the outer one is much the larger. The interosseous ridge and the 
tracts for the attachment of the muscles are also situated more 
distally, but the most noticeable difference between the species is the 
extreme robustness of the fossil form. 
The minimum antero-posterior diameter of the radius of the 
living species is 3.5 mm., whereas, in the bone of the fossil species 
