250 
TERTfART YERTEERATA OF THE EAYOir. 
tliat Fraas’s restoration of the snout is correct) the distance of the posterior border of 
the nares from tlie occipital crest would he represented by 70, in Prozewjlodon by 
63, and in Zeu(jlodo)i osir/s hy 51. Other points in which this skull differs from that 
o{' Protocetiis arc : (1) the rostrum is much broader and more massive, and does not 
narrow suddenly in front oi pm. 3 ; (2) the nasals are rather shorter and are separated 
posteriorly by a process of the frontals ; (3) the supiaocci|)ital surface is perhaps a 
little less concave from side to side. From the skull of ZeiKjlodoii osiris this form is 
also distinguished by: (1) a relatively rather stouter rostrum and generally more 
heavily built skull ; (2) the possession of much longer nasals, separated posteriorly 
by a process of the frontals — this nasal process of the frontals does, however, exist in 
some species of the genus (see J. Muller, pi. vii. fig. 2); (3) having a very much 
less concave supraoccipital surface ; (4) the greater inflation of the cranial region 
of the skull. 
A plaster cast of the brain-case, taken from an imperfect skull, agrees fairly well, 
Palatal view of left preinaxilla and maxilla, with piu.'.i and pm. 4, of Pruzcwilodoti airov. 
(•., alveoln.s of canine; f., fossae for the reception of the jioints of the lower teeth; i. 1-3, alveoli of llu' 
incisors ; i.r., inner roots of jinn. 3 and 4 ; m. 1, first molar ; 7nx., maxilla ; pm. 1-4, premolars or their 
alveoli; pmx., premaxilla; s., suture for union with palatine, g uat. size. 
SO far as it goes, with a natural brain-c.ist described by Dr. Elliot Smith in his ptiper 
on the “ Brain of the Arclneoceti ” *. In this he states that the natural cast dilfers so 
far from the artificial cast taken from a skull of Ztiujlodon oatns that it must have 
helonged to an animal differing gencrically from that form. 
Upper l)e)itilion (El. XXI. hgs. 1 a, I n ; text-fig. 82). — There are three incisors, 
which, judging from one of which the crown is well jireserved, were conical sharp- 
])ointed teeth directed somewhat forwards. 'I'lie crown is somewhat compre^ssed 
laterally, and there is a slight keel on the anterior and posterior borders; the eiiaimd 
at the base of the crown is raised into line ridges. The first incisor is situated at the 
extreme anterior end of the prernaxllla, the others follow at intervals of about T5 cm. ; 
* Proc. lloy. Soc. vol. 7J (1003) p. 322. 
