HISTORY OF THE MARSUPIALIA 635 



however, or in the older Parana, but abundant material 

 representing those of the Santa Cruz has been collected. 

 Among these there was a considerable range of size and some 

 variety of structure, and they all differed in certain respects 

 from the modern Australian genera, differences which have led 

 some authorities to deny the marsupial character of all these 

 South American forms. The differences are of three kinds : 

 (1) there are no vacuities in the bony palate; (2) the milk- 

 dentition is less reduced, the canines and one or two premolars 

 being changed ; (3) the enamel of the teeth, in the only genus 

 (fBorhycena) which has been examined microscopically, resembles 

 in its minute features that of the placentals and lacks the 

 marsupial characters. Though by no means unimportant, 

 these differences are altogether outweighed by the thoroughly 

 marsupial nature of all other parts of the skeleton, and I can- 

 not but agree with Dr. Sinclair ^ in including them in the same 

 family with the Tasmanian Thylacine. 



The genus j Prothylacynus was especially like the latter 

 and must have had a very similar appearance, though in the 

 restoration (Fig. 297) the colour-pattern is changed to one of 

 longitudinal stripes, as more probably pertaining to so ancient 

 and primitive a form. The humerus had the epicondylar 

 foramen, and a large vestige of the hallux was retained, though 

 it could not have been visible in the living animal. 



A more specialized Santa Cruz genus was ^Borkycena 

 (Fig. 244, p. 494), an animal of about the same length and height 

 as -fProthylacynus and the Thylacine, but much more massive 

 and powerful. The skull was remarkable for the small size 

 of the brain-case and the great spread of the zygomatic arches, 

 which gave a rounded and almost cat-hke appearance to the 

 head, as is shown in the restoration (Fig. 244). In this genus 

 the upper incisors were reduced to three, a very unusual thing 

 among the Polyprotodonta, and the humerus had lost the 



1 Reports of the Princeton University Expeditions to Patagonia, Vol. IV, 

 Pt. 3. 



