372 PATAGONIAN EXPEDITIONS I PALEONTOLOGY. 



overestimating the lengths of the posterior caudals. It may have pos- 

 sessed less flexibility than is indicated in the drawing. No trace of a 

 clavicle has been preserved, and it may have been rudimentary, as in 

 Thylacynus, (Cunningham, p. 2, 1882) and not attached to the acromion. 

 It has been supplied in the restoration from analogy with existing car- 

 nivorous marsupials. The length of the back has been determined by 

 comparing the length of the dorsal series in Thylacynus with the lengths 

 of the posterior lumbars in that genus and Prothylacymts. The depth of 

 the chest is doubtful, as none of the longer ribs are completely preserved. 

 Habits. It may be inferred from the large pointed claws that Prothy- 

 lacynus was more active in attacking prey than Borhycena. The greater 

 degree of outward deflection of the metacone spur in the upper molars 

 indicates a more completely carnivorous habit than in the latter genus. 

 The reduction of the hallux is an adaptation to terrestrial progression. 



PROTHYLACYNUS PATAGONICUS Ameghino. 



(Plates XLVII-LI ; LII, Figs. 3, 5 ; LIII, Figs. 5-8 ; LIV, Figs. 2, 2, 8, 9, 14; LXI, Fig. 2.) 



Prothylacynus patagonicus Amegh.; Nuevos Restos Mamif. F6s. Patagonia 

 Austral, p. 26, Aug., 1891 ; Revista Argentina Hist. Nat. I, entr. 5^, 

 p. 312, Oct., 1891. 



The preceding account of the osteology of Prothylacynus is based al- 

 most entirely on the remains of a single individual of the classic species 

 Prothylacynus patagonicus (No. 15,700) from the Upper Santa Cruz beds 

 at Killik Aike. A reference to the discovery of this unique specimen will 

 be found in Mr. Hatcher's Narrative of the expeditions (this series, Vol. 

 I, pp. 53, 54). The American Museum collection contains a fragment of 

 the right maxilla with the second, third and fourth molars in place (No. 

 9561 Am. Museum), also from Killik Aike. As a description of the 

 anatomy of the hard parts has already been given, it remains only to 

 tabulate the principal measurements. 



MEASUREMENTS. 



Cranium, length, condyles to anterior orbital border . . . . . .138 



palato-narial border to condyles, inclusive . . . .109 



least width of brain case ........ -0175 



Skull, greatest width across arches . . . . . . . . . 1 20 



Occiput, height .0485 



" width at base .......... .057 



