Fig. 5. A, Eoproterotherium inaequifacies, third upper molar—natural size; C, Protherotherium karaikense, third upper molar—natural size, after Ameghino.

Notodiaphorus gen. nov.

The basis of this genus is particularly a hind limb found associated which is much less developed than the Santa Cruz genus Diadiaphorus to which it is most nearly related. These two genera are unique in having the ectal facet on the astragulus developed in two planes so that it appears as a deep notch. In the case of the new genus the toes are almost equal in size, giving us a stage in the development of this three-toed form which is much more primitive than the well-known Santa Cruz genus.

Notodiaphorus crassus sp. nov.

Fig. 6. Distal end of right
humerus—½ natural size.

The specimen selected as type is number 3287 of the Amherst Collection, consisting of a complete pes, tarsus, lower end of the tibia, and the femur, from the Deseado on the Chico del Chubut River, west of Puerto Visser. Beside this, there are seven other specimens, mostly parts of hind limbs, but others having also the lower end of the humerus, the radius and ulna, metacarpals, and some phalanges. The species is distinguished by its large size, being larger than the species of the Santa Cruz, and, at the same time, the three toes of both the pes and the manus are subequal in size.

The distal end of the humerus associated indirectly with this species is moderately heavy, with fair-sized epicondyles, and no entepicondylar foramen. The supratrochlear fossa is moderately deep, the anconeal very deep, the two being connected by a small foramen, as is typical for this family. The trochlearis, slightly oblique to the long axis of the shaft, has a simple pulley-like articular end without ridges of division, the internal border being narrower and higher than the external.

Measurements, Specimen 3201
Humerus,greatest diameter of the distal end58 mm.
width of trochlea on the anterior side37 mm.
width of trochlea on the posterior side28 mm.