SINCLAIR I 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 . lepidus). 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 (PL LXIII, fig. 4$). 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. 
15,706. 15,707. 15,708. 15,709. 15,068. 15,624. 15,999. 
Length of mandible from tip of 
median incisor to M^- inclusive .0175 
.017 
Length of mandible from posterior 
border of median incisor alveolus 
to M-j- 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 
Ml, antero-posterior “ 
.002 
.002 
“ transverse “ 
.0018 
.002 
Ml, antero-posterior “ 
.0015 
.0015 
No. 
9122. 
