352 PATAGONIAN EXPEDITIONS: PAL/EONTOLOGY. 



A peculiar feature noted by Ameghino (1894, pp. 112, 113) is the 

 annular character of the vertebral epiphyses. A low round prominence 

 from the centrum projects through the central perforation of the epiphysial 

 ring. This structure is most typically developed in Borhycena, occurring 

 less regularly in Frothy lacynus. 



Parts of several ribs are preserved with No. 15,701, of which the two 

 most complete specimens are figured (Pis. XLV, fig. 4; XLVI, fig. i). 

 The smaller of these, the second rib of the left side, is shorter than in 

 Thylacynus, but slightly more robust and with thicker distal end. The 

 larger rib (PI. XLV, fig. 4), from the cylindrical character of its shaft, 

 evidently belongs near the middle of the thorax. The proximal end is 

 more robust than any of the ribs in this region in Thylacynus. The shaft 

 also is more cylindrical. 



Part of the sternum is preserved with the remains of both species of 

 Borhycena in the collection. The presternal segment (PI. XLV, fig. 5) 

 differs from the corresponding element in Thylacynus in having the dis- 

 tal portion of the posterior bar narrower and deeper. The mesosternal 

 segments are shorter and proportionately narrower than in the recent 

 genus. 



Appendictdar Skeleton. The scapula (PI. XLVI, fig. 2), although 

 smaller than in Thylacynus, has the neck of about the same length. The 

 glenoid cavity is circular in outline and the coracoid process large, with 

 the tip directed inwardly to about the same extent as in the Tasmanian 

 genus. The high scapular spine divides the external surface into two 

 unequal fossae, of which the anterior is the larger. Its surface is almost 

 flat. The infraspinous fossa is deeply concave with elevated axillary 

 border. The inferior angle is more acute than in Thylacynus. The 

 scapular spine terminates in a long narrow acromion, the tip of which is 

 missing. The supraspinous fossa is perforated by a large foramen. In 

 Thylacynus several foramina pierce the base of the scapular spine, open- 

 ing into the infraspinous fossa. These are represented by a single large 

 foramen in Borhycena. In both genera a small foramen pierces the 

 anterior margin of the neck near the middle of the suprascapular notch. 



The radius (PI. XLV, figs. 2, 2a) is of the same length as in Prothyla- 

 cynus, but differs considerably in shape and is much less robust. The 

 head is transversely flattened and elliptical in outline. The articular sur- 

 face for the ulna is deeper than in Thylacymis and less confined to the 



