ON A NEW SPECIES OF MACRAUCHENIA (M. BOLIVIENSIS) 411 
more nearly than that of any other Mammal. But, on the whole, I 
think it must be admitted that the resemblance of the back of the 
skull of the .J/acrauchenia to that of Auchenza is sufficiently close to 
justify the conclusion, that the predominance of the Cameline type, 
so marked in the neck, was maintained in the head of the extinct 
Mammifer. 
The fossil which remains for description (Plate VI., [Plate 32] fig. 4) 
consists of two fragments of the matrix (@ and 4), which fit together, 
and to which adhere certain portions of the upper jaw and palate, 
together with the fractured remains of three grinding-teeth and part 
of the alveolus of a fourth, all of the right side, and in a continuous. 
series. The alveoliand part of the crowns of these teeth are contained 
in the larger fragment of matrix,—the smaller fragment fitting against 
the larger and the teeth which it contains, and exhibiting the impres- 
sions of the grinding surfaces of three teeth and of their inner faces, 
a portion of dental substance adhering to the latter, in the case of the 
two anterior teeth. Of the hindermost tooth nothing is left but the 
impression of one fang. 
The impression of the grinding surface of the first tooth is nearly 
four-tenths of an inch long, convex from before backwards, concave 
internally: the outer boundary of the impression is broken away, a 
fragment of dental substance adhering to the posterior part of its 
inner face. The part of the larger portion of the matrix (a) which 
should contain the alveolus of this tooth is absent. The antero- 
posterior extent of the coronal impression of the second tooth is a 
little more than o'4 of an inch; it is concave from before backwards 
externally, nearly flat internally, and shelves with a slight convexity 
upwards and inwards. The inner boundary of the impression is, as in 
the preceding case, markedly concave ; and a much larger fragment 
of tooth-substance adheres to it. The outer boundary of the im- 
pression is broken away, but much more in front than behind, where 
its width is fully o-4 of an inch. The impressed line which separates 
this impression from the next is convex forwards. Corresponding 
with this impression there are, in the larger fragment of matrix, an 
almost entire conical posterior fang, about o'4 of an inch long, lodged 
in a complete bony alveolus, whose outer wall is broken away, and 
the posterior half of a similar alveolus for an anterior fang: there is 
no trace of a third alveolus or fang; and, indeed, there seems to be 
no room for one. The fang which exists is connected below with a 
portion of the crown; but this is so broken, that all that can be 
remarked of it is its marked internal convexity. 
The coronal impression of the third tooth is half an inch long ; 
