LOWER JAW, OF MACRAUCHENIA PATACHONICA. 
81 
assumption by the premolars of the molar type of grinding-surface to the last of the 
premolar series, the antecedent premolars retaining the single-lobed crown ; from Palceo- 
theriu'M it further differs, as before observed, in the retention by the last molar of the 
two-lobed structure. In Artiodactyles, and especially the ruminant section, all the pre- 
molars have a simpler structure with the smaller size of crown. 
From the figures by Bravard * we learn that Macrauclienia , like marry other tertiary 
mammals, retained the type dentition, viz. i c j={, p 4 ^, m^|= 44, and that, as in 
Anoplotherium and Dicliodon , the series was unbroken by any notable interval, not any 
of the teeth having a crown much higher or longer than the rest. 
Description of the Plate. 
PLATE VIII. 
Fig. 1. Portion of left mandibular ramus with the^> 2 -to 3 grinders: outside view. 
Fig. 2. do. do. do. : inside view. 
Fig. 3. Grinding-surface of the teeth. These figures are of the natural size. 
Fig. 4. Entire mandible with the p 3 -to 3 grinders, and a restoration of the missing 
’teeth: outside view, reduced view: from Bravard, op. cit. 
Fig. 5. p 3 -to 3, inside view; similarly reduced: from Bravard, op. cit.. 
Fig. 6. Grinding-surface of second upper molar (to 2), right side, restored to the natural 
size: from Bravard’s plate. [The upper molars (to 1,. to 2) of Macrauclienia , 
as of Nesodon , are penetrated by three folds of enamel on their inner side, 
which, deepening as they extend, are soon interrupted by wear, and the ends 
converted into islands. In to 2 (Plate VIII. fig. 6) the mid fold is of unequal 
depth and becomes reduced to two islands of enamel (e, h). In to 1 the island 
(/j) of Bravard’s specimen is not shown, but this maybe because the tooth is 
more worn. In to 3 the insular end of the fold ( k ) remains beyond the fold, 
which continues as in to 2 : the mid fold is represented by a single island, and 
the third fold ( d ) is short. The outer lobe (f, h) is turned, as usual, in to 3, 
so that the surface (f) looks outward and backward, with concomitant con- 
traction of the hind part of that molar. 
The last premolar (p 4) is like a small molar, but shows only two enamel- 
islands on its inner half : p 3 has a mid indent on the outer side and indications 
of two shallow folds on the inner side ; it has lost breadth, but retains fore- 
and-aft extent ; p 2 is still more narrowed transversely, has an even outer 
surface, and a single fold of enamel on the inner one which runs forward. This 
fold is represented by a notch in p 1. The premolars decrease in breadth, and 
in a minor degree from before backward, as they approach the canine, 
— B,. O., March 1870.] 
* Op. cit. 
MDCCCLXX. M 
