440 PATAGONIAN EXPEDITIONS I PALEONTOLOGY. 



of the crown. In the Princeton specimen there are six ridges. On the 

 inner side, the fourth ridge extends inferiorly but a short distance, as is 

 well shown in the figure (PI. LXIV, fig. 30). In addition to the main 

 anterior ridges, five short ribs are observable on the outer side of the sec- 

 torial. These probably extended farther toward the cutting edge, but 

 have been partly obliterated by the abrasion of this part of the tooth 

 crown from contact with the opposing tooth in the upper jaw. The pho- 

 tograph referred to above shows two short faint ridges back of the last 

 prominent outer rib. These, however, do not give rise to serrations on 

 the margin. The crowns of the vestigial antemolars have not been pre- 

 served, but in the photograph of the type specimen are seen to be antero- 



FIG. 9. 



a 



Abderites crassignathm, right ramus of mandible, x f (No. 15,425). a, side view ; b, crown 



view. 



posteriorly elongated and to overhang in front, as in Palceothentes minutus 

 (PI. LXIII, fig. 46). The fourth vestigial tooth and the posterior pre- 

 molar are in contact. The third and fourth vestigial teeth are separated 

 by a considerable diastema. The alveoli of the first and second are elon- 

 gated antero-posteriorly and inclined obliquely forward, as in Palceothentes. 

 A large mental foramen pierces the mandible below the sectorial, and 

 another is present, below or slightly posterior to the third vestigial ante- 

 molar. 



MEASUREMENTS. 



No. 15,425. No. 75,079. 



Length, posterior border of incisor alveolus to M^ . . . .022 

 " of space occupied by vestigial antemolars . . . .0095 

 " " molar series on alveolar border .... .013 .013 



Posterior premolar, antero-posterior diameter .... .0007 



