202 
PATAGONIAN EXPEDITIONS I PALAEONTOLOGY. 
forms a root and does not continue to grow throughout life. In the 
material before me I have found nothing confirmatory of this statement, 
though I am not in a position to question it. The molars differ quite 
constantly from those of Nesodon in a few particulars ; the anterior lobe 
or crescent is relatively somewhat broader and the posterior lobe nar- 
rower than in the larger animal, but the difference is not great. All of 
the lower grinding teeth have, in fact, a curiously narrow, slender 
appearance. 
Milk Dentition (Pis. XVII, figs. 7-9; XVIII, figs. 2, 3). — The tem- 
porary teeth differ but slightly from those of Nesodon and the functional 
milk-incisors are almost identical in the two genera, but di- and the 
upper canine are even smaller in Adinotherium , the former especially 
being a mere slender style ; the canine is larger than di-, but still very 
small. In the accessible material of Adinotherium , in which the milk- 
premolars are considerably abraded, I can detect no tangible difference 
from those of Nesodon , except that in dp- only two spurs, instead of three, 
project into the principal valley, and that the posterior valley is smaller, 
as is also the case in its permanent successor. Unworn teeth would 
probably show greater differences. 
Prelacteal Dentition. — As yet, I have seen no well-preserved examples 
of the prelacteal dentition in this genus, but one individual indicates that 
Fig. 39. 
Adinotherium ovinum : Left premaxilla with permanent incisors and prelacteal i— , X x- 
this dentition was present, at least in part. This animal, which is shown 
in text-fig. 39, retains the small, quill-like, prelacteal upper tusk, which 
is external to the permanent i- and cannot possibly be di-, as it is far 
too small, and of an entirely different form. 
Skull (Pis. XX, figs. 1-4; XXVI, fig. 2). — Aside from its smaller size 
and lighter construction, the skull of Adinotherium is so very closely like 
that of Nesodon , that it is difficult to find any tangible points of distinc- 
