438 
PATAGONIAN EXPEDITIONS I PALAEONTOLOGY. 
Length of molar series on alveolar border 
Width of base of incisor ..... 
Depth “ “ “ “ 
Posterior premolar, antero-posterior diameter 
“ “ transverse “ 
M t , antero-posterior diameter .... 
“ transverse “ . 
Mg-, antero-posterior “ . 
“ transverse “ . 
Mg-, antero-posterior “ . 
“ transverse “ . 
Depth of mandible below first molar . 
ABDERITINAE. 
No. 15,710. No. 9594. 
.010 
.002 
.003 
.0012 
.001 
.00475 
.005 
.0024 
.002 5 
.003 
.003 
.002 
.002 
.002 
.0015 
.005 
.005 
ABDERITES Ameghino. 
(Plate LXIV, Figs. 3, 3a ; Text Fig 9, a, b.) 
Abderites Amegh. ; Enum. Sist. Especies Manfif. Fos. Patagonia Austral, 
p. 5, 1887. 
Diprotodont marsupials in which the first lower molar is developed as 
a striated sectorial blade resembling superficially the sectorials of the Plagi- 
aulacidse. 
Dentition (PI. LXIV, figs. 3, 3# ; text figs. 9, a, b ). — The formula 
for the lower dentition is ]TTT - r The median incisors are not preserved 
in either specimen of Abderites crassignathus in the Princeton collection 
(Nos. 15,079, 15,425), but, judging from the size of their alveoli, they were 
large teeth. The posterior premolar is a very small, single-rooted, cylin- 
drical tooth closely applied to the anterior root of My. Between the 
enlarged incisor and the posterior premolar are alveoli for four single- 
rooted, vestigial teeth. The molar series is placed very obliquely to the 
long axis of the jaw, more so than in any other member of the Csenoles- 
tidae, the anterior blade of the first molar projecting beyond the plane of 
the outer surface of the mandible. The molars are double-rooted and 
decrease in size posteriorly, as in all the Caenolestidae. The first has been 
converted into a very perfect sectorial by the complete obliteration of the 
metaconid, the great elevation and lateral compression of the protoconid- 
paraconid blade, and the development of parallel vertical ridges on both 
the outer and inner faces of the crown. The ridges on opposite sides 
