1893.] Fossil Mammalia of Southern Patagonia. 441 
munculus patagonicus, in the lowest bed of the Santacruzian 
formation. This skeleton is imbedded in a large block of 
stone, and, as yet, only a few bones have been exposed. The 
lower jaw has been taken out almost intact, with its entire 
dentition. This new specimen, the preservation of which 
leaves nothing to be desired, shows that the jaw is not so nar- 
row nor so compressed as I have figured recently in drawing 
from a specimen whose symphysis was evidently distorted by 
pressure. In the new specimen now at hand, the distance 
between the internal posterior border and the second true 
molar on each side is 10 mm., 5. It thus results that the two 
dental series are more widely separated at the back, and that 
the whole jaw is much more elevated. 
The exact dental formula is I 3, C+, P M.§,M%. The first 
two true inferior molars are very nearly of the same size, but 
the third is smaller. The internal incisors are weaker than 
the external ones. The canine is a little more developed than 
in the first specimen, and is separated from the premolar by 
a small diastema. It is probable that the two specimens are 
respectively male and female. Unfortunately, the individual 
represented by the new specimen, was very old, so that one 
can no longer detect the details of the surface of the crown of 
the molars. The dental series measure, in a straight line, 31 
millimeters. The femur is 11 centimeters, and the radius 95 
millimeters long. The humerus has a large epitrochlear per- 
foration, but it lacks the intercondylar foramen. Each of 
these bones, in form, are those of a man in miniature. 
Among the other forms belonging to the Santacruzian for- 
mation, and which ought to be better known, I will select only 
the most important, beginning with the Ungulates which are 
exceedingly interesting. 
IL 
I have been able to reconstruct the foot of the Mesorhinidæ 
(the genera Mesorhinus, Theosodon, Pseudocoelosoma), which 
are the predecessors of the Macraucheniidæ. The genus Theoso- 
don had five toes in front as well as behind ; the three in the 
middle were well-developed, very similar to those of Macrau- 
