128 PATAGONIAN EXPEDITIONS: PALAEONTOLOGY. 



The humerus (Plate XXVI, fig. 2) is long and slender, with small 

 hemispherical head, which presents proximally more than posteriorly ; the 

 external tuberosity is low, broad and massive, with an articular facet for 

 the acromion ; the inner tuberosity is small and the bicipital groove is deep 

 and narrow ; the deltoid ridge is a large and very prominent, shield-shaped 

 area, which projects more than in Sclerocalyptus, less than in the Santa 

 Cruz armadillos ; the supinator ridge is also prominent and extends very 

 far proximally; the external epicondyle is very small, while the inner 

 one is large and is perforated by a large foramen, as in Sclerocalyptus, 

 Panochthtis and Dcedicurus, but not in Glyptodon; the trochlea is wide 

 and low, with a convexity for the head of the radius and prominent inner 

 flange ; the anconeal fossa is small and shallow. 



The radio-cubital arcade is longer and wider than in the Pampean 

 genera and there is no such rugosity or interlocking of the interosseous 

 crests as occurs in them. The radius (Plate XXVI, fig. 4) is very short, 

 hardly more than one half as long as the humerus, and quite slender, 

 closely resembling that of Proeutattis in form ; the head is transversely 

 expanded and has three facets for the humerus, a median concavity and 

 two lateral, nearly plane surfaces, quite as in the last named genus ; the 

 facet for the ulna is a broad, slightly convex band, which occupies nearly 

 the whole posterior side of the head ; the shaft is slender and laterally 

 compressed, thickening gradually to the broad distal end ; the carpal sur- 

 face is large, concave and undivided ; on the inner side of the distal end 

 is a prominent tubercle for ligamentous attachment. 



The ulna (Plate XXVI, fig. 3) is much larger than the radius in every 

 dimension ; the olecranon is less elongate than in the armadillos, tapering 

 but slightly to the proximal end, which is moderately thickened and in- 

 curved ; the inner side of the process is deeply grooved ; the sigmoid 

 notch is broad, rather shallow and not oblique to the long axis of the 

 bone, on the inner side it extends around the head of the radius and 

 beneath the humeral trochlea; the shaft is short, stout, straight and of 

 nearly uniform diameter, except for the interosseous crest on the distal 

 half and a moderate expansion of the distal end, which bears a large 

 facet for the pyramidal and a small one for the pisiform. 



The carpus (Plate XXVI, fig. 5) is broad and very short proximo- 

 distally, but the bones have not acquired the massive, block-like shapes 

 seen in the Pampean genera. The scaphoid is the smallest bone of the 



