ON A NEW SPECIES OF MACRAUCHENIA (M. BOLIVIENSIS) 405 
Vicugna ; but, relatively to its width, it is much shorter and stouter 
than this bone in either the Guanaco or the Vicugna. There are no 
longitudinal ridges on the surface of the vertebra below the pre- 
zygapophyses, in which respect AZ. Boliviens?s differs from J/. Pata- 
chonica, and approaches the Aauchent@. The anterior articular facet 
of the centrum is concave from above downwards, in consequence of 
the projection of the thickened and convex lower third of that face; 
the posterior facet is not only concave from above downwards from 
a similar cause, but is also concave from side to side. The con- 
cavity of both articular facets is greater than in JZ. Patachon‘ca, and 
the present species departs, in these respects, more widely than the 
latter does from the Auchenie. 
The astragalus (Plate VI. [Plate 32.] fig. 2)—This bone is, again, 
quite that of the Patagonian species in miniature, differing chiefly in 
the proportions of its dimensions, as shown by the subjoined table :— 
Macrauchenta Boliviensis. M. Patachonica.  Guanaco. Vicugna. 
in. in. in. in. 
Length . . . 145 3°3 16 13 
Greatest width . 1:2 29 12 85 
Greatest depth .  °85 215 95 8 
If we take the lengths of the astragali, it will be observed that 
their proportions in the Bolivian and Patagonian Macraucheni@é are 
not the same as those of the cervical vertebra. The astragali bear 
the ratio of 1:24, while the cervical vertebrae gave 1:13. Further- 
more, the proportions of length, width, and depth in the two astra- 
gali are different. Like the cervical vertebra, the astragalus of JZ. 
Boliviensis is a, relatively, stouter bone than that of the Vicugna; 
though instead of being shorter it is a little longer, occupying a 
position, in point of absolute length, between the astragalus of the 
Vicugna and that of the Guanaco. As the astragalus thus yields 
results agreeing very well with those given by the cervical vertebra, 
we may safely assume that not only the absolute size, but the pro- 
portions of the body of Macrauchenita Boliviensts were nearly those 
of the existing Llamas, and differed widely from those of the heavy 
and huge Macrauchenia Patachonica. 
The tibta—What remains of the bones of the hind leg confirms 
this view of the proportions of Macrauchenia Boliviensis. 1 have the 
proximal end of the left tibia, minus the fibula, and with the outer 
articular condyle broken away. Below this point, the outer edge 
and surface of the fragment are uninjured, and the posterior face is 
in good preservation, but the internal face is somewhat crushed. 
