HOG-TRIBE. 561 



201 . Hyracotherium.{\) — In the Hyracotherium leporinum, an animal 

 about half the size of the Peccari, the upper canines were compressed 

 and directed downwards : the typical number of premolars, (which 

 probably are transitorily represented in the Peccari) was here constant, 

 the first of the four being situated near the middle of the diastema 

 between the canine and the second premolar ; like the latter it 

 had a simple subcompressed short conical crown with an anterior 

 and posterior basal talon and two fangs. The third and fourth 

 premolars suddenly assume an increased size and complication 

 of crown, resembling the two last premolars in the Peccari : they 

 present one internal and two external cusps, with two inter- 

 mediate smaller tubercles, and a cingulum or basal ridge almost 

 surrounding the entire crown. Each true molar (PI. 140, fig. 6) 

 has the four principal and the two accessory cusps, as in 

 the Peccari, but the anterior and posterior basal ridges are 

 united by internal and external ones so as to form a cingulum, and 

 the last molar is not longer, and is narrower posteriorly, than the 

 penultimate one : no vestige now remaining of the characteristic 

 predominance of size of the last molar in the typical Suida. Each 

 principal cusp of the molars in the specimen described by me had 

 its summit worn into a little pit. The dentition of the lower jaw 

 and the incisive formula of the Hyracotherium are as yet unknown. 



202. ChfETopotamus. — The Chcsropotamus Cuvieri{2) was about one 

 third larger than the Peccari, and deviated further than the Hyraco- 

 there in a direction towards the Hippopotamus. All the premolars 

 were more simple in comparison with the true molars ; the last 

 premolars had each an external large and an internal low and small 

 tubercle, both inclosed by the cingulum. The true molars are each 

 like two premolars combined, and with the inner tubercles developed 

 to equality with the outer ones ; they have also the two small 

 intermediate tubercles and a well-developed cingulum (PL 140, 

 fig. 5) : the last upper molar resembles that of the Hyracothere in 

 form and proportions. In the lower jaw the canine had much of the 

 form and proportions of that of a Carnivore. There are three 



(1) Geological Transactions, 2d Series, Vol. vi, p. 203, PI. 21. 



(2) Geological Transactions, 2d Series, Vol. vi. p. 41, Pi. 4. 



O O 



