This is a group of large land birds, comparable in size to the great moas of New Zealand which apparently arose, flourished, and died out in South America. In the Santa Cruz they were abundant, the best known form being P. inflatus, a bird some six feet high; while the largest, P. longissimus, had a head nearly twice as long and limb bones half again as large as this species; so that it represented a bird nine to ten feet high. Previously but one specimen of this type, a part of a mandible, has been found in the Deseado beds. We were fortunate enough to find the greater part of a femur, indicating a bird equal to the largest of those in the Santa Cruz. There are also toe bones of Phororachus of a size about the same as P. inflatus.

A host of names, generic and specific, have been given to the individual bones of the birds of this type, but Ameghino, in studying the birds of the Santa Cruz, brought them all together under the single genus Phororhacus. (See Bol. Inst. Geog. Argen., 1895, t. 15.) Referring to the single bone in the Deseado, however, he gave it a new generic name Physornis, which differs from Phororhacus only in the lower jaw being more convex, but should stand until better material has been found to establish whether it differs enough to be entitled to generic independence.

Physornis fortis Ameghino.

P. fortis Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p. 576.

Under this specific name Ameghino describes a part of the lower jaw 150 mm. long which he says equals in size Phororhacus longissimus, and differs only in the greater convexity of the mandible. Our specimen is a femur, apparently of the same bird, being of the type of Phororhacus and about the size of P. longissimus; so I have placed it in this species.

This femur is of large size, moderate length, and has a shaft subcylindrical in section. The distal end is expanded and the condyles are flattened, the inner one being the wider, the outer condyle being narrower and the external margin projecting to make a high ridge. The pit on the posterior side of the shaft just above the condyles is unusually deep and of large size. On the anterior side there extends from either condyle a low marginal ridge which soon fades into the contour of the shaft. Between these ridges there is a wide shallow furrow which also loses itself above in the convex surface of the shaft.

Fig. 149. Right femur, back view—½ natural size.