SINCLAIR: MARSUPIALIA OF THE SANTA CRUZ BEDS. 439 



meet along the edge of the " sectorial blade in a series of serrations, the 

 number of which varies with the species. The broad talon is bicuspidate. 

 The second and third molars are quadrangular in outline and bunolopho- 

 dont, with the paraconid present but reduced. The fourth molar is 

 retained in one specimen (No. 15,425); but the crown has been abraded 

 to a flat surface without trace of cusps or ridges. 



In the fragment of the right maxillary referred by Ameghino (1898, p. 

 184, fig. 49, II; 1903, p. 142, fig. 64, p. 178, fig. 107) to A. meridion- 

 alis, the second molar is fully quadritubercular, in contrast with the in- 

 completely quadritubercular M- in Palcepthentes. 



Mandible. The mandible is much deeper than in Callomenus and 

 Decastis. The coronoid is high, with the anterior margin sloping back- 

 ward. Its base is perforated by a branch of the alveolar canal opening 

 externally behind the last molar (PI. LXIV, fig. 30). The masseteric 

 fossa is broad and occasionally pierced by a small foramen situated some 

 distance below the large irregular opening shown in the figure (PI. LXIV, 

 fig. 3), which is due to fracture. The symphysis is broad and heavy, ex- 

 tending posteriorly beneath the first molar. 



ABDERITES CRASSIGNATHUS Ameghino. 



(Plate LXIV, Figs. 3, 30; Text Fig. 9.) 



Abderites crasignathus (sic] Amegh. ; Revista Argentina Hist. Nat., I, p. 



248, 1891. 

 Abderites crassiramis Amegh. ; Rev. Gen. des Sciences, p. 80, fig. 4, 1893. 



The beautiful little specimen figured on PI. LXIV (No. 15,079) was 

 collected by Mr. Hatcher on the Rio Chalia, and has been mentioned by 

 him in the Narrative of the expeditions (this series, Vol. I, p. 113). A 

 second specimen from Killik Aike (No. 15,425) agreeing with the first in 

 proportions, but lacking the crown of the sectorial, is referred to the same 

 species and is represented in Fig. 9. 



A. crassignathus is readily identified by the presence of five or six 

 prominent ridges on the anterior half of M T . The ridges are developed 

 on both the outer and inner sides of the tooth, producing a series of ser- 

 rations on the cutting edge of the sectorial blade. A photograph of the 

 type in the Ameghino collection obtained by Professor Scott shows five 

 prominent ridges on the outer side of Mr extending to the cutting edge 



