riiOZEUGLODON. 
251 
behind and external to the sockets of i. 2 and i. 3 there are slight pits for the reception 
of the ti])s of the lower incisors. The canine, represented hy its alveolus only, was a 
very largo tooth, much larger than the incisors : this seems to be a ])rimitive character 
inherited from the Croodont ancestor. The first ])remolar is a single-rooted tooth, 
separated from the canine by an interval of about 1'5 cm., in which, to the outer side, 
is a pit for the lower tooth. In the skull described, p?n. 1 is just being cut, its point 
ajipearing in the middle of the alveolus of the deciduous tooth it is replacing ; this seems 
to he the first instance in which any indication of a succession of teeth has been observed 
in the Zeuglodonts. The second premolar is separated from the first by an interval of 
1'5 cm., occupied hy a deep pit ; it is a double-rooted tooth with a strongly compressed 
high cutting-crown ; the anterior edge bears four or five small serrations, while on the 
hinder edge are two larger accessory denticles and a third smaller one belonging to the 
cingulum. Behind, and to the inner side of the posterior root of this tooth there is a 
deep fossa for the lower tooth. The third premolar is also a large high cutting-tooth, 
the crown of which is similar to that of pm. 2, except that on its inner side a little 
behind the middle point there is a prominent enamel-covered buttress, projecting 
inwards and backwards and supported hy a large distinct root ; the presence of a third 
root in this and the following tooth distinguishes this genus from Zeuglodon. In one 
specimen there is also a small accessory root on the outer side of the tooth between 
the two main outer roots. The last premolar differs from pm. 3 in having a more 
molariform crown, the posterior border sloping much less steeply away and the three 
posterior denticles rising nearly to the same height ; on the anterior border the two 
accessory denticles are larger than on the anterior teeth. This tooth also has a large 
inner buttress and root. The first molar is considerably smaller than pm. 4 ; there 
seems to have been only one accessory denticle on its anterior border, while behind 
the main cusp there are two rising to nearly the same height, so that the edge of the 
posterior part of the crown is nearly horizontal. This tooth also had a postero-internal 
buttress, but it is relatively smaller than in the posterior premolars, and it is not clear 
whether it had a distinct root or is borne on the inner part of the transversely 
elongated posterior root, imperfectly divided by a vertical groove. 
If these teeth be compared with those of Protocetus, they are found to be widely 
dissimilar. In that genus the dentition, so far as the premolars and molars are 
concerned, is practically that of a Creodont, the serration of the cutting-edges of these 
teeth, so characteristic of the later Zeuglodonts, not having been acquired in that early 
type. At the same time the posterior cheek-teeth {pm. 3-m. 3) possess an inner (third) 
root and distinct indications of an inner tubercle, both completely wanting in Zeuglodon. 
In Prozeuglodon the structure of the posterior premolars [pm. o, pm. 4), and probably 
also oi m. 1, is exactly intermediate, the characteristic serration having been attained 
while the inner (third) root is not yet lost. The posterior molars seem to be lost, or 
at least to be undergoing reduction. The large size of the canine compared with the 
2 K 2 
