SINCLAIR : MARSUPIALIA OF THE SANTA CRUZ BEDS. 395 



small intermediate cuspules may be observed in unworn teeth, as in Micro- 

 biotherium and Dasyurus viverrinus. The outer cusps are high and coni- 

 cal. The paracone is relatively higher than in Thylacynns and the meta- 

 cone shear strongly developed, but less rotated outwardly on M 1 than in 

 the latter genus. A large antero-external style is always present. On 

 M 1 the protocone, paracone and antero-external style are functional. The 

 protocone is large and basin-shaped, as in the anterior molars. The high 

 conical paracone is connected with the antero-external style by a sharp 

 ridge, producing a transverse shear, as in Dasyurus, but less perfectly so, 

 owing to the relatively greater elevation of the paracone. In some indi- 

 viduals of A. manzaniana a small metacone is present. With decrease in 

 size of the metacone, the root supporting it is greatly reduced and may 

 disappear entirely, producing a double-rooted tooth. The anterior molars 

 are triple-rooted in both species. 



The lower incisors are similar to those of Thylacynus and Dasyurus 

 with rather thick crowns divided by a transverse groove (PI. LX, fig. 30). 

 The second tooth on either side is displaced behind the median and 

 lateral pair. The canines are shorter and less robust than those of the 

 upper series, with conical crowns curved to about the same extent as in 

 Thylacynus. The lower premolars are simple-crowned, double-rooted, 

 piercing teeth, of which the median and posterior are subequal in size. 

 The heel cusp on the anterior premolar is small, becoming larger on the 

 median and posterior pair (PI. LX, fig. 20.]. The anterior premolar is 

 spaced on either side. The median and posterior premolars may be in 

 contact or slightly spaced. The molars increase regularly, not only in 

 size, but in the height of the external cusps. They are closely crowded, 

 so much so that the heel of each is impressed into the anterior surface of 

 the tooth next succeeding. In MT, the arrangement of the cusps is linear, 

 but in the second, third and fourth the paraconid is more and more de- 

 flected internally, producing a shear which cuts against the metacone spur 

 of the upper teeth. The protoconid is high and conical, becoming flattened 

 on the posterior side by shearing against the anterior face of the trigon of 

 the upper molars. The lobate, blade-like paraconid is separated by a 

 narrow slit from the protoconid. The heels are broad and strongly bi- 

 cuspidate, the lingual cusp corresponding to the undifferentiated hypo- 

 conulid-entoconid. A short antero-external cingulum is present on the 

 second, third and fourth molars. 



