372 PATAGONIAN EXPEDITIONS: PALAEONTOLOGY. 
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 
Thy lacy mis, (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 Pro.thylacynus. 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 Bor hy ana. 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 ; LI I, Figs. 3, 5 ; LIII, Figs. 5-8 ; LIV, Figs. 2, 2 a, 8, 9, 14; LXI, Fig. 2.) 
Prothylacynus patagonicus Amegh. ; Nuevos Restos Mamif. Fos. Patagonia 
Austral, p. 26, Aug., 1891 ; Revista Argentina Hist. Nat. I, entr. 5a, 
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 oT 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 . . . . . . . . .120 
Occiput, height 0485 
“ width at base 057 
