130 
TERTIARY VERTEBRATA OF THE FAYtM. 
Family PAL^OMASTODONTID.E. 
In the skull the nasals shortened and the external nares somewhat shifted back 
from the end of the snout. Mandible with elongated spout-like symphysis, projecting 
beyond the skull. A single pair of large incisors (^. 2) in both upper and lower jaws. 
Upper incisors in form of downwardly-directed tusks, with a band of enamel on their 
outer side ; lower incisors procumbent and continuing forwards the upper surface of 
the spout-like symphysis. Premolars replacing milk-molars in both upper and lower 
jaws ; molars with not less than three transverse ridges. 
This family includes the Eocene genus PaUeoinastodon and the Miocene Tetrahelodon, 
possibly also the problematical Phiomia. The species range in size from little larger 
than Mceritherium to nearly as large as the existing Indian Elephant. 
Genus PAL.fflOMASTODON, Andrews. 
[Tageblatt des V. Interna tionalen Zoologen-Congresses, No. G, p. 4, Berlin, 1901 
(Verhaiullungen, }>. 528, 1902).] 
Skull with sagittal crest ; nares just in front of orbit. Dental formula : — 
/. ; c. ; 'inn. | ; m. ^ . Last premolar bilophodont ; molars trilophodont. Neck 
more elongated than in Plephas] limb-bones, so far as known, much like those of the 
later Proboscidea. 
This genus is at present known only from the Upper Eocene Fluvio-marine beds of 
the Fayiim, where it is represented by several species, the type being Palceomastodon 
beadnelli. The several species are distinguished by (1) difference of size ; (2) the 
form of the symphysis and its position with regard to the anterior ])remolars ; (3) the 
degree of development in the last lower molar; (4) the degree of development of 
secondary tubercles in the molars. 
The Skull (Pis. NIL, XIII. ; text-figs. 48, 49 A). — Though differing widely in general 
appearance and in many details from that of the later Elephants, the skull is 
nevertheless typically Proboscidean in all essential points of structure, and may be 
described in short as that of a very dolichocephalic Elephant. Some of the more 
obvious differences between it and the skull oi FAephas are : — (1) the relatively small 
though still considerable development of the bone cells and sinuses in tlie upper 
and hinder region of the cranium ; (2) in correlation witli the last character the 
presence of a sagittal crest, which extends to a point about over the middle of the 
temporal fossa, where it divides into two supratemi)oral ridges, which run forwards 
and outwards and probably terminated in the postorbital ])rocesses of the frontal; 
(3) the elongation of the hauls cranli and })articularly also of the palatal region, 
