SINCLAIR: MARSUPIALIA OF THE SANTA CRUZ BEDS. 433 



As characters of specific value may be mentioned the small size, shal- 

 low, slender jaws, the presence of a well-marked anterior accessory cuspule 

 on the last upper premolar, and the great length of the space occupied 

 by the vestigial antemolars, which are less closely crowded than in some 

 of the larger species (P. lepidiis]. These teeth are of an exceedingly 

 peculiar shape. The first and second of the series are widely separated 

 from each other at the roots, but the cylindrical crowns curve forward 

 abruptly, lying prone on the alveolar border in such a manner that the tip 

 of the second rests on the root of the first, while the tip of the latter rests 

 on the base of the median incisor (PI. LXIII, fig. \b\ The last vestigial 

 tooth has a small, button-shaped crown overhanging anteriorly. Minute 

 notches in the edges of the median incisors are due to accidental fracturing 

 of the attenuated edges of the enamel layer investing the outer surface 

 of the crown. 



Two large mental foramina are usually present, situated respectively 

 beneath the last vestigial tooth and the first molar. 



A photograph of the type specimen of Palceothentes simplex in the Ame- 

 ghino collection, for which the writer is indebted to Professor Scott, 

 shows no differences warranting a separation of this species from P. 

 minutus. 



MEASUREMENTS. 



No. No. No. No. No. No. No. No. 

 15,706. 15,707. 15,708. 15,700. 15,068. 15,624. 15,000. 9122. 

 Length of mandible from tip of 



median incisor to Mj inclusive .0175 .017 

 Length of mandible from posterior 

 border of median incisor alveolus 

 to M 7 inclusive . . ..013 .013 

 Length of space occupied by vesti- 

 gial teeth and posterior pre- 

 molar 0064 -0057 



Width of base of median incisor .0008 .0008 .0008 .001 

 Depth " " " " " .0014 .0014 .0013 .0015 



Length of superior molar series on 



alveolar border . . . .006 



Ml, antero-posterior diameter . .0024 



" transverse " . .002 



M^, antero-posterior " . .002 .002 



" transverse " . .0018 .002 



M- 3 -, antero-posterior " . .0015 .0015 



