410 ON A NEW SPECIES OF MACRAUCHENIA ML. BOLIVIENSIS) 
be obtained. Side by side with them I give the corresponding 
measurements of the skull of the Vicugna :— 
; AL, Boliviensis. Vicugna. 
Transverse diameter of the occiput oa in. in. 
the outer edge of one paramastoid to 19 2°25 
that of the other . : : “ 
Ditto from the outer edge of one anaes, . i 
condyle to that of the other re ? 
The transverse diameter of the occipital | 7 7 
foramen 
It will be observed that the two series of dimensions correspond 
very closely, the two latter being identical, while the A/acrauchenia 
appears to have had even a narrower skull than the Vicugna. In 
form, the occiput of Macrauchenia agrees better with that of the 
Llamas than with that of any other ungulate animal with which I 
have compared it. 
Thus, in an old Guanaco I find an equally well-marked ridge in 
the middle line of the supra-occipital element ; the occipital crest is 
equally prominent, though not so stout; the sagittal crest is as well 
marked, thin and sharp, and, as in Macrauchenia, its superior edge 
ascends. There is a fossa between the occipital condyle and the 
paramastoid, similar in form to that in AMacrauchenza, though much 
shallower. The occipital condyles are very much alike; and their 
relation to the precondyloid foramina is the same in both cases. 
The paramastoid has the same proportional breadth ; and its greatest 
diameter is, in both cases, directed from without and behind, inwards 
and forwards: in both cases its inner edge is peculiarly thickened. 
Again, the paramastoid of the Awchenia, like that of the fossil, is 
very short, its apex hardly extending below the level of the occipital 
condyle. 
The occiput of Macrauchenia, on the other hand, differs from that 
of Auchenia in the much greater thickness of the supra-occipital, 
which in the Macrauchenia has fully double the thickness of the same 
region in an old Guanaco, whose skull is much larger—in this respect 
approaching the Sheep and some other Ruminants, which have this 
bone very thick. The supra-occipital, also, is much higher, in pro- 
portion to its width, in A/acrauchenia than in Auchenia; its lateral 
contours are parallel, and not divergent outwards and upwards. 
There is nothing in the AZacrauchenia resembling the deep notch 
between the supra-occipital and the base of the paramastoid, into 
which a part of the mastoid fits in Awchenza. In contour, in fact, 
the occiput of the Wacrauchenia resembles that of the Palgotherium 
