Sinclair: marsupialia of the santa cruz beds. 363 
but the root of the second tooth in the series is seen to be displaced 
behind the median and lateral members. The tip of the canine is miss- 
ing, and the crown is broadly grooved on the inner side. The premolars 
are closely crowded. The anterior tooth is in contact with the canine and 
lies obliquely to the long axis of the jaw. The crowns of all the lower 
premolars are laterally compressed, with large, simple heels. The median 
and posterior teeth are of the same size. As in the superior series, the 
molars increase rapidly in size posteriorly. In the first molar the pro- 
toconid, paraconid and heel are in line. In the remaining teeth, the 
paraconid is deflected more and more internally, forming with the pro- 
toconid a powerful shear against the inner side of the metacone spur of 
the upper molars. The protoconid is high and conical, with a sharp 
anterior edge. It is separated from the lower and more blade-like para- 
conid by a deep cleft. The heel of M T is far more reduced than in 
Thylacynns , inclosing a shallow basin with a single high point on its 
posterior rim. On the anterior molars the heel is narrower and flatter 
than in Thylacynus , with a single prominent cusp at its posterior extremity. 
The hypoconid is greatly reduced, more so than in Cladosidis. The 
prominent cusp mentioned above occupies the position of the hypoconulid. 
The entoconid is smaller than in Thylacynus and scarcely distinguishable 
as a separate cusp. A small antero-external, shelf-like cingulum is de- 
veloped on the second, third and fourth molars. 
Skull (Pis. XLVII ; XLVIII, figs. 1, ia, 3). — As in all the Santa Cruz 
thylacynes, the skull is large in proportion to the size of the body, 
although relatively less so than in some of the smaller genera. The 
brain case is long, low and narrow, considerably depressed in the region 
above the tentorium and greatly constricted postorbitally. The facial 
region has been almost entirely destroyed by weathering, but was probably 
not unlike Borhycena and has been so represented in the figure (PI. 
XLVII). Enough is preserved to show the single, moderate-sized infra- 
orbital foramen, situated above the posterior premolar, and the imperforate 
facial expansion of the lachrymal. The zygomatic arches are robust and 
intermediate in degree of expansion between Borhycena and Amphipro- 
viverra. The orbits are not placed as far forward as in the latter genus, 
their anterior border coinciding with a line drawn through the posterior 
root of the second molar. 
Parietal and supraoccipital exhibit the same relationship as in Borhycena. 
