178 
PROFESSOR FLOWER ON A NEWLY DISCOVERED 
running from base to apex of the crown, rather nearer the anterior than the posterior 
edge of the tooth. The canine (c) is of similar form to the incisor, but of larger size. 
The first premolar (p 1) is also formed on the same plan, i. e. with a smooth and rounded 
external surface, and the internal surface with an anterior and posterior depression, 
separated by a vertical ridge, and bounded below by the cingulum. The second pre- 
molar (p 2) is wider from before backwards, the hinder part being more developed; 
its external surface has a deep groove passing from near the posterior part of the base 
upwards and forwards, with a gentle sigmoid curve to the apex, dividing the surface 
into an anterior and posterior area, of which the anterior is the larger. An indication 
of this groove exists in the first premolar of the right side. The inner surface has the 
vertical ridge increased in thickness, and a smaller ridge behind which isolates the pos- 
terior concavity. The cingulum is well developed and notched ; on the outer side it 
sends up a row of small prominences from its border. 
The transition from the second premolar (p 2) to the first true molar (to 1), through 
the third and fourth (p 3 and p 4) premolars, is very gradual, being effected, as in the 
upper teeth, chiefly by the lengthening out of the posterior part of the crown. The 
first and second true molars are almost exactly alike, but the second is slightly the 
larger ; the difference in the appearance of their grinding-surface is simply the result 
of difference of wear. They are elongated from before backwards and much compressed. 
Their base is surrounded by a well-marked cingulum. The outer surface is, generally 
speaking, flat, but divided by a shallow vertical groove into an anterior and posterior 
area, each convex from before backwards, the anterior being about half the width of 
the posterior. The inner side is divided by a much deeper vertical groove ( to s ), running 
obliquely forwards as it penetrates the tooth so as nearly to meet the base of the 
external groove, and cutting the tooth into two lobes, each of which is further divided 
on the inner side by a much less marked depression (as and^s). In other words, the 
inner side of the tooth may be described as consisting of two columns (a i c and p i c ), 
each of which doubtless terminated in conical cusps in the unworn tooth, separated 
by a deep oblique indent (ms), and bounded before and behind by shallower indents 
(a s and p s ), marking off anterior and posterior accessory columns (a t and p t) at each 
extremity of the tooth, 
The posterior tooth is unfortunately injured; but the whole of the outer wall remains 
intact, with enough of the inner side to show that it is formed on precisely the same plan 
as the others ; but its hinder part is slightly more elongated and compressed, though 
without any additional lobe as in many Ungulates. 
Comparison of the teeth and taxonomic inferences . — There can be no doubt that the 
dental characters of Homalodontotherium warrant our placing it within the order Ungu- 
lata. Whether Perissodactyle or Artiodactyle may be at first sight less obvious. The 
evenness of height and unbroken continuity of the teeth is no test, as it is shared by the 
Artiodactyle Anoplotherium with the Perissodactyle Macrauchenia. A better criterion 
is the character of the premolars as compared with the molars. In every known Artio- 
