396 PATAGONIAN EXPEDITIONS: PALAEONTOLOGY. 



Only fragments of the sacrum have been recovered, enough, however, 

 to show that the spines were long and separate, not fused into a contin- 

 uous ridge. Nothing is known of the caudal vertebrae, but the fragments 

 of the sacrum indicate that the tail was probably long and well developed. 



The ribs likewise are represented by more or less fragmentary remains, 

 which appear to be shorter, more slender and less curved than in Myo- 

 castor, and to have rather more resemblance to those of Agouti; the anter- 

 ior ribs are broader and more compressed laterally, the posterior ones 

 more slender and rod-like. The sternum is entirely unknown. 



Appendicular Skeleton. The scapula is high and rather narrow, with 

 slender neck and no coraco-scapular notch ; the spine appears to be nearly 

 in the middle and to divide the blade into almost equal pre- and post- 

 scapular fossae, the former perhaps somewhat broader. (In the restoration, 

 Plate LXX, the scapula is incorrectly restored, the prescapular fossa being 

 made too narrow and the coracoid border forming too definite an angle 

 with the suprascapular. Probably the shape was more like that seen in 

 Agouti.'] A very marked difference from Myocastor and Capromys con- 

 sists in the shallowness of the notch, "incisura colli," which determines 

 the length of the acromion ; in the two recent genera this notch is ex- 

 tremely deep, while in the fossil it is much shallower, as is clear, despite 

 the fact that in none of the specimens is the acromion preserved, for the 

 distal extension of the spine is shown. The coracoid, though hardly vis- 

 ible from the side, is yet quite large, forming a slender, incurved hook. 



In the humerus also we find greater resemblance to Agouti than to 

 Myocastor; the shaft is relatively long and, for most of its length, is 

 strongly compressed laterally ; its thickness, which is considerable in the 

 proximal portion, diminishes distally ; the deltoid hook, so conspicuous in 

 Myocastor and Capromys, is entirely absent ; the trochlea is broad and, 

 anteriorly at least, is covered entirely by the radius and consists of three 

 parts, a narrower external and broader internal concavity and a pro- 

 nounced convexity between them ; there is, however, no interruption of 

 the articular surface. The supratrochlear fossa is large and deep and is 

 perforated by a fontanelle, while the anconeal fossa is smaller ; the epicon- 

 dyles are very inconspicuous and there is no entepicondylar foramen. 



The fore-arm bones are of moderate length, the ulna about equalling 

 the humerus in this respect, and they are thus somewhat shorter than in 

 Myocastor. The radius has a broadly expanded head, which occupies the 



