570 
PROFESSOR OWEN ON EOSSIL REMAINS OE EQUINES 
and parallel in position, as in Palceotheriwn ; the fold g, as in E. neogmus , is less deep 
than in E. arcidens ; the posterior ridge bounding the posterior outer longitudinal 
channel, f, is not developed in E. principalis (at least in the representative molar 
of that species). The more important differences above defined are so well marked 
in this tooth as to lead to the inference that they would more or less characterize the 
whole upper molar series. Whether, or in what degree, the entire tooth was curved is 
not known. 
I regret that I have no specimen of the lower molars of Equus arcidens. Dr. Lund 
figures the grinding-surface of the second true molar, left side, under jaw, of his E. neo- 
gceus {tom. cit., IV. tab. xlix. fig. 5, copied in fig. 14, Plate LXIL), which shows as marked 
and interesting a departure from the pattern of the grinding-surface of these teeth in 
other Equines as does the upper molar. The external mid cleft {i) is deep and simple ; 
and the outer surface of the two divisions of the molar ( a , b) are regularly convex and 
to a degree corresponding with the concavities of the same part in the answering divi- 
sions of the upper molars, as shown in Plate LXII. fig. 9, at f,f. The entering folds 
(fig. 1 4, k, g) at the inner side of the lower molar simply curve backward, do not expand 
terminally, and are wider at their beginning than in other Equines. Fig. 4. 
There is barely a trace of the mid internal indent, /, fig. 4, of the 
Equus fossilis, from the Oreston Cavern (Cut, fig. 4), and in the figures 
of the Equine lower molars illustrative of the present Paper and its 
predecessor, and as in E. aff. caballo (=E. curvidensX , Plate LXII. 
fig. 15). Thus we have, in E. neogceus, as we most probably should Lower molar, p 4, 
have in E. principalis and E. arcidens , lower molars retaining more Equus fossilis. 
of the type of such teeth in Paloeotherium and Rhinoceros than they do in ordinary 
recent and fossil Equines. 
In my 4 Odontography ’ I described and figured the molar series of the left ramus of 
a lower jaw, found fossil in the Pampas Deposits at Buenos Ayres, as being of a Macrau- 
chenia , from the indications of the affinity of that genus to the perissodactyle section of 
Cuvier’s Pachyderms which had been detailed in the first account of that singular 
genus*. The subsequent discoveries of M. Bravard of parts of Macrauchenia , including 
the entire skull and dentition, confirmed the accuracy of that determination of the 
lower molars and of the generic distinction of the extinct animal. 
* “ In the ungulate series there are hut two known genera (the Rhinoceros and Paloeotherium) which, like 
the quadruped in question, have only three toes on the fore foot. Again, in referring the Macrauchenia to the 
tridactyle family of Pachyderms, we find towards the close of our analysis, and by a detailed comparison of 
individual hones, that the Macrauchenia has the closest affinity to the Paloeotherium. But the Paloeotherium , like 
the Rhinoceros and Tapir, has the ulna distinct from the radius, and the fibula from the tibia ; so that even if 
the Parisian Pachyderm had actually presented the same peculiarities of the cervical vertebrae as the Pata- 
gonian one, it would have been hazardous, to say the least, while ignorant of the dentition of the latter, to refer 
it to the genus Paloeotherium. Most interesting, indeed, will be the knowledge, whenever the means of obtaining 
it may arrive, of the structure of the skull and teeth in the Macrauchenia.” — The Zoology of the Voyage of 
H.M.S. ‘ Beagle ,’ Part I., Fossil Mammalia, 4to, 1840, p. 54, pis. vi.-xv. 
