362 PATAGONIAN EXPEDITIONS I PALAEONTOLOGY. 



PROTHYLACYNUS Ameghino. 



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



Prothylacynus Amegh.; Nuevos Restos. Mamif. F6s. Patagonia Austral, 

 p. 26, Aug. 1891 ; Revista Argentina Hist. Nat. I, entr. 5^, p. 312, 

 Oct., 1891. 



This genus, so frequently mentioned in previously published discussions 

 of the relationships of South American and Australian marsupials, is 

 represented in the Princeton collection by the remains of one individual 

 referable to the species Protliylacynus patagonmis (No. 15,700), comprising 

 an incomplete skull, mandible, parts of both scapulae, humerus, both radii, 

 ulna, pelvis, both femora, tibia, fibula, patella, part of the hind foot, the 

 scaphoid and a few phalanges of the fore foot, six cervicals, four dorsals, 

 three lumbars, the sacrum, five caudals and fragments of the ribs and 

 sternum. The -exceptionally perfect state of preservation of this material 

 permits full comparison with living forms and indicates in no uncertain 

 fashion the true relationships of the animal, a discussion of which will be 

 found on a later page. 



Dentition (Pis. XLVII ; XLVIII, figs, i, 2). --The greater part of the 

 facial region of the skull has been weathered away, invoking the incisors, 

 canines and the anterior and median premolars. In the side view (PI. 

 XLVII), these have been supplied from Borhycena. Prothylacynus dif- 

 fers, however, in possessing an additional upper incisor (Ameghino, 1894, 

 p. 121). The posterior superior premolar is a stout, double-rooted tooth, 

 with a broad heel without heel cusp. It is considerably smaller than this 

 tooth in Thylacynus. The first, second and third molars increase rapidly 

 in size posteriorly. In M 1 and M-, the protocone is a well-developed 

 bunoid cusp, but is absent in M-, although the inner root supporting this 

 part of the tooth crown is larger than in the preceding molars. The 

 antero-external style, the only one of the outer row of styloid cusps 

 remaining, is considerably larger than in TJiylacynns. With this excep- 

 tion, the outer cingulum is entirely wanting. The fourth molar is more 

 reduced than in Thylacynus. The protocone is represented by a broad 

 smooth surface. The metacone is vestigial and the posterior root sup- 

 porting it almost obliterated. The high conical paracone is connected by 

 a sharp ridge with the antero-external style. 



In the mandible, the crowns of the three incisors have been broken off, 



