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 Thylacynus and the meta- 
cone shear strongly developed, but less rotated outwardly on M- than in 
the latter genus. A large antero-external style is always present. On 
M- 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 (PL LX, fig. 3 a). 
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. 2 a). 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 M T , 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. 
