656 



ANNUAL EEPORT SMITHSONIAN INSTITUTION, 1908. 



Fig. 11. — Tooth of 

 Mceritherium (X h)- 



Those of the upper jaw were dagger-like and downward!}^ projecting, 

 while the lower ones were directed forward, their combined upper 

 surface forming a continuation of the spout-like union or symphysis 

 of the jaws. The molar teeth, 24 in number, bore 

 on the crown four low tubercles partially united 

 into two transverse crests. The neck was of suffi- 

 cient length to enable the animal readily to reach 

 the ground, though the prehensile lip must have 

 been used for food-gathering. Our knowledge of 

 the creature's bodily form is imperfect, as a com- 

 plete skeleton has not been found. Mceritherium measured about 

 3^ feet in height, and existed up into the Upper Eocene as a contem- 

 porary of PalceoTYiastodon^ doubtless owing to a continuation of those 

 favorable conditions under which it lived. 



Palceomastodon. 



Palo'oinastodon of the Upper Eocene was more elephant-like than 

 its predecessor, Mceritherium^ and of larger size, while its limbs were 

 much like those of more modern types, 

 materially in height, 

 with a considerable de- 

 velopment of air cells 

 in the bones. The small 

 nasals with the nasal 

 openings had receded so 

 that they lay just in 

 front of the orbits, much 

 as in the tapir of to-day. 



This would imply the J/^^^ ^i 



development of a short 



The skull has increased 



-Skull of Palceomastodon ( X 

 Andrews. 



,>5) ; after 



extensile proboscis, es- fig. 12. 

 sentially like that of the 

 modern elephant except for size. The upper and lower canines and 

 incisors have entirely disappeared, except the second paid of incisors 

 in each jaw, which have become well-developed tusks. Those of the 

 upper jaw are large, downwardly curved, and 

 with a band of enamel on the outer face. The 

 lower jaw has elongated considerably, especially 

 at the symphysis, and the lower tusks point 

 directly forward as in Mceritherium. The pro- 

 boscis possibly did not extend beyond the lower 

 tusks while at rest, though it could probably 

 be extended beyond them. The premolar teeth 

 have two while the molars have three transverse crests composed of 

 distinct tubercles, and the cingulum of the hindermost tooth shows 



Fig. 13. — T o o t h of 

 Palceomastodon (X i). 



