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PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



[Nov. 21, 



Perissodaetyle Mammal, and lead one, at once, to seek its analogue 

 among the Artiodactyla ; and of these the lluminants alone, so far 

 as I know, offer anything like it. The inner grinding-surface of 

 any true molar of a Euminant, however, exhibits two ridges and 

 three depressions; while that of the Macrauchenia has only one ridge, 

 with a concave shelving depression behind, and doubtless, in the 

 perfect condition, another in front ; in other words, it has the con- 

 tour exhibited by one of the hinder premolars of a Euminant. The 

 inner division of a posterior premolar of Auchenia has its convex 

 inner surface undivided by any vertical depression ; and its outer, 

 posterior margin exhibits no marked inflexion : but such an inflexion 

 exists in the corresponding teeth of the Giraffe and of many Deer, 

 in some of which latter a vertical groove, dividing the inner face 

 into two convexities, may also be noted. 



I am of opinion, therefore, that the tooth in question is a poste- 

 rior premolar, and that it was constructed upon the Euminant type. 

 In this case, however, the dentition of Macrauchenia must have 

 departed widely from that of the €amelidce ; for there were certainly 

 two teeth with flat grinding crowns in front of that just described, 

 which would give, at least, three premolars in all, or as many as are 

 found in ordinary lluminants. 



I am strengthened in the conviction that there were as many as 

 three premolars, by the rest of the structure of this interesting frag- 

 ment. Within the series of teeth just described, in fact, it presents 

 a considerable portion of the roof of the palate, some of whose bony 

 matter remains. At a distance of half an inch from the inner wall 

 of the posterior premolar, a longitudinal sutural line traverses the 

 whole length of the palatine surface, and ends abruptly (in conse- 

 quence of the fracture of the matrix) as well behind as in front. 

 Its posterior end is 1*2 of an inch behind a transverse line drawn at 

 the level of the posterior margin of the last premolar. Opposite and 

 behind this tooth, the right half of the palate is marked by what 

 might hastily be taken for a suture, but which is nothing but a frac- 

 ture. Behind it, and 0-9 of an inch in front of the posterior end of the 

 longitudinal suture, two curved transverse lines, convex forwards, 

 which I believe to be the maxillo-palatine sutures, pass into the 

 longitudinal suture. 



Thus, it is clear that the palate must have extended back for 1-2 

 of an inch behind the third grinding-tooth. 



Supposing this tooth to have been succeeded by three others whose 

 length, if they were molars, would be probably between 0-6 and 

 0*7 of an inch, it follows that the posterior margin of the palate 

 must have extended, at least, as far back as the posterior margin of 

 the second molar. This is further than it extends in the Auchenia; 

 (the very forward extension of whose palatine aperture is excep- 

 tional among the Artiodactyla), but it is not so far as in the Camel, 

 where the posterior boundary of the palate is opposite the middle of 

 the last molar*. 



* The attempt to differentiate the Artiodactyla and Perit.tr/dactyhi absolutely 

 by the position of the posterior margin of the bony palate is fallacious. On an 



