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. [Illustration: Fig. 6. Distal end of right humerus—½ natural 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 end 58 mm. width of trochlea on the anterior side 37 mm. width of trochlea on the posterior side 28 mm. [Illustration: Fig. 7. Right radius and ulna, distal end of ulna from specimen No. 3275—½ natural size.] [Illustration: Fig. 8. Left femur posterior side—½ natural size.] The radius and ulna were from another specimen which, however, was associated with a typical astragulus. The two bones are long, slender, strongly curved, and in contact with each other throughout their entire length, so that there could have been no rotary movement of the forearm. The radius is a slender bone with the proximal articular facet relatively small, the facet being slightly concave, of ovoid outline and with the transverse diameter the greater. There is but a tiny band-like facet for the ulna situated on the posterior side near the inner margin. Distally, the radius widens into a heavy end with a rugose area on the outer side for contact with the ulna, and with two distal facets, a larger for the scaphoid, and a smaller for the lunar, the two being separated by a low ridge. The ulna is heavier above, with a strong backwardly directed olecranon process. The sigmoid notch makes almost a semicircle, the articular surface being broad and extending well onto either side of the bone. The facets for the radius are tiny. The distal end of this bone is wanting. MEASUREMENTS, SPECIMEN NO. 3275 Radius, length 251 mm. greatest width at proximal end 28 mm. greatest width at distal end 36 mm. least diameter of shaft 16 mm. [Illustration: Fig. 9. Distal end of left tibia—½ natural size.]