EUTRACHYTHERUS SPEGAZZINIANUS 81 
with a marked tendency to become vestigal. The suture 
of the premaxilla comes to the base of inc. 3. There fol- 
jiows a short diastema, then a tiny alveolus for the canine, 
closely followed by the first premolar which is also small. 
The second premolar shows no inflexion. Beginning with 
the third premolar there is a strong inner inflexion, which 
in the fourth premolar and molars is bifurcated. The 
molars are considerably larger than the premolars, the 
second being the largest of the series. With each succes- 
sive molar, the inflexion is wider, so that in m. 3 the tooth 
is divided into three lobes of nearly equal size. All pre- 
molars and molars are rootless, curved, and set so deep in 
the jaw that they almost meet in the median line. A typi- 
cal molar measures 50 mm. in length, of which only 7-8 
Pe 35> 
Fig. 48. E. spegazzinianus, right upper dentition—natural size. 
mm. project above the border of the jaw. All the back 
teeth are covered with a thick coating of cement. 
The arrangement of the teeth of the lower jaw is shown 
in fig. 25 h., after Ameghino. The first and second incisors 
are greatly enlarged. Incisor 3 is lacking, and the canine 
vestigal. Pm. I is small and single-lobed, the succeeding 
premolars and molars being large and divided into two lobes 
by a deep external, and a shallow internal infolding. 
MEASUREMENTS 
Skull, width between the orbits 60 mm, 
Skull, width across the postorbital processes 88 mm. 
Skull, height from m. 2 to top of frontal 77 mm. 
Skull, width of palate opposite inc. 2 42 mm. 
Skull, width of palate opposite m. 2 62 mm. 
Dentition, length inc. 1 to m. 3 140 mm. 
Dentition, incisor I ant.—post. length 11 mm. width 16 mm. 
Dentition, pm. 3 length If mm. width 13 mm. 
Dentition, m, 2 length 22 mm. width 16 mm. 
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