HISTORY OF THE PROBOSCIDEA 433 



lower tusks were still shorter and procumbent, pointing straight 

 forward, and were covered with enamel, which was very thick 

 on the lower side and thin or wanting on the upper. All of 

 the grinding teeth were in place and function at the same time, 

 which was not true of any of the genera previously considered, 

 and each of the premolars had its predecessor in the milk-series, 

 which it succeeded and displaced in the normal vertical manner. 

 The premolars were smaller and simpler than the molars, 

 which were made up of three pairs of conical tubercles arranged 

 to form a three-crested crown. The skull, as compared with 

 that of the elephants, was long and narrow, the premaxillaries 

 extending into a long snout ; the nasals were shortened, 

 though not so much as in the succeeding genera, and there was 

 probably rather a long and flexible snout than a true proboscis. 

 The skull had a long and well-defined sagittal crest, which 

 none of the later genera had, and the development of sinuses 

 in the cranial bones, though considerable, was much less than 

 in the elephants. The occiput was relatively high and the 

 thickened parietals did not tower above it to any such degree 

 as they do in the elephants. The symphysis of the lower jaw 

 was greatly prolonged, extending out beyond the ends of the 

 upper tusks, and this implies that the lower lip had a corre- 

 sponding prolongation. 



The skeleton is still incompletely known, though it may be 

 said that the neck was probably longer than in the subsequent 

 genera of the family. The limb-bones were already proboscid- 

 ean in character, differing only in details from those of the 

 more typical members of the order, but the animal was more 

 lightly built and had less massive limbs. The presence of the 

 third trochanter on the femur, which is lacking in all of the 

 succeeding forms, is an interesting approximation to other and 

 still more primitive groups of ungulates. The several species 

 of jPalceomastodon represent a considerable range in size, 

 from animals which were not much larger than a tapir to those 

 which equalled a half-grown Indian Elephant. 



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