SINCLAIR: MARSUPIALIA OF THE SANTA CRUZ BEDS. 377 



pie, laterally compressed blade, with a rounded heel, but without heel cusp. 

 The median premolar is a replica of the anterior tooth on a larger scale. 

 The posterior premolar is enlarged, with a prominent, piercing protocone 

 and a broad heel, with distinct heel cusp. The prominence of the latter 

 varies with the amount of wear to which this part of the tooth crown has 

 been subjected. The first, second and third molars have the protocone 

 well developed. It is slightly cupped in unworn teeth. On M 1 , the pro- 

 tocone is reduced to a small conical cusp, while the paracone and antero- 

 external style are enlarged, and the metacone is vestigial. In the anterior 

 molars, the proportions of the dental cusps are much the same as in Pro- 

 thylacymis, except that the protocone of M- is well developed. 



In the inferior series, the incisor crowns show considerable lateral com- 

 pression, but are so badly worn in all the specimens examined that their 

 original shape cannot be ascertained. As in many recent carnivorous 

 marsupials, the root of the second tooth in the series is displaced pos- 

 teriorly with respect to the roots of the median and lateral incisors. The 

 canines are reniform in cross-section owing to the presence of a broad 

 groove on the lingual side. The anterior surface of the crown is flattened 

 (PI. LVI, fig. i ; LIX, figs. 7, fa) apparently to accomodate the tooth to 

 the narrow groove in the premaxilla, into which its point is received when 

 the jaws are brought into occlusion. The amount of spacing between the 

 lower premolars varies somewhat in different individuals of the same 

 species, the greatest amount of variation in this respect occurring in the 

 width of the space between the median and posterior premolars. The 

 anterior and median premolars closely resemble the corresponding teeth 

 in the superior series. Each consists of an enlarged piercing central cusp 

 and a round heel. In unworn teeth, the heel of the median premolar sup- 

 ports a small conical heel cusp. A minute anterior basal cuspule is also 

 present. In worn teeth, the heel is reduced to a broad convex area, and 

 the identity of the anterior cuspule is lost The posterior premolar is 

 enlarged like the corresponding tooth opposing it in the superior series. 

 In unworn specimens a conical heel cusp is present. Characters of 

 generic importance appear in the heels of the lower molars. The same 

 rapid increase posteriorly in the size of the molar crowns is to be noted 

 as in Borhycena and Prothylacynus. The cusps of the trigonid are iden- 

 tical in shape and position with those of the latter genus. In the anterior 

 molars, the heel supports a shallow, basin-shaped depression, bounded by a 



