1847. | OWEN ON ENGLISH EOCENE MAMMALIA. 23 
and it might have been inferred, therefore, from the bilobed figure of 
the tooth now determined to be the last milk-molar, that the last true 
molar must also have had a bilobed crown, if even the state of the 
specimen had not permitted the actual demonstration of this generic 
distinction from the Paleotherium, as in fig. 4, M 3. 
Thus the specimen in question having belonged to an individual at 
almost the greatest age compatible with the retention of the deciduous 
molars, gives the dental formulee of the lower jaw of both the imma- 
ture and adult states of the species: e. g.— 
Deciduous or milk-teeth: 7. 3—3; c.1—1; m. 4—4. 
—_- 
Permanent teeth: 7. 3—3; ¢. 1—1; p. 3—33 m. 3-3. 
The animal has perished, in fact, at that age when the jaws contain 
the greatest number of molar teeth, not less than twenty, for example, 
being lodged in the lower jaw in question. The teeth in use are the 
four milk-molars, and the first and second true molars on each side: 
those still concealed in the jaw are the three premolars and the last 
true molar. The premolar which is wanting to complete the nor- 
mal number is that which should have succeeded the first deciduous 
molar, and which would have answered to the first small premolar 
in the true Paleotheria* : I have therefore indicated the three pre- 
molars that are developed in Paloplotherium by the same signs as 
those which designate their homologues in the Paleotherium+. The 
non-succession of D 1 bya P 1, and its displacement together with D 2 
by P 2, is a modification in which Paloplotherium resembles Equust : 
and this instance of affinity is extremely interesting in connexion with 
the approach made by certain Paleeotheres (Pal. Aurelianense, e. g.) 
to the monodactyle character of the Horse, by the disproportionate 
size of the middle of the three toes on each foot. 
In the comparison of a detached true molar of the present Palzo- 
therioid with the typical species, since the character of the bifid middle 
internal lobe would be lost by a moderate amount of wear of the 
crown, and since the tubercle terminating the hinder ridge would be 
obliterated by a further extent of abrasion, it may be remarked that 
lower grinders of the Paloplotherium may be distinguished by the 
absence of the basal ridge along the inner side of the crown, as well 
as of that which, in the true Paleeotheres, unites the anterior and 
posterior oblique ridges along the outer side of the base of the crown. 
A portion of lower jaw from the Hordle Cliff (PI. IV. fig. 1), of a 
younger animal than the above-described, having the four milk-molars 
(D 1-4) and the first true molar (M 1) m place, showed by the cha- 
racter of the crowns of these teeth, and especially by that of the per- 
manent true molar, its distinction from the typical Paleeotheres, and 
its specific identity with the Paloplotherium above-described from the 
same stratum and locality. 
The crown of the second true molar was found almost completely 
* See my ‘ Odontography,’ pl. 135. fig. 6. p 1. + Jb. 
t Jb. pp. 572, 580, pl. 136. figs. 4 & 5. 
