96 THE MAMMALIA OF THE DEEP RIVEK BEDS. 



but angulate, running inward at a right angle from the external wall and then turn- 

 ing at an obtuse angle towards the hypocone ; somewhat external to the latter it 

 sends off a spur which connects with the posterior cingulum. The posterior valley 

 is thus completely enclosed, even before the tooth is worn down. There is, properly 

 speaking, no posterior pillar, its place being taken by a triangular depression, which 

 is enclosed between the hypocone, the spur from the posterior crest already mentioned, 

 and the elevated cingulum. 



B. Lower Jaw (PI. Ill, Fig. 25). As in the upper series, the incisors diminish 

 from the median to the lateral. Seen from the front, they are much like the upper 

 teeth, but differ from them in having no well-marked internal cingulum and conse- 

 quently no invagination such as occurs in the European form. The canine is rather 

 small, possibly a sexual character, and follows the incisors with hardly an interval. 



The first premolar is smaller, especially transversely, than the corresponding 

 upper tooth and is very simply constructed. It is narrow and compressed, and con- 

 sists of a low principal cusp (protoconid) with obscurely marked anterior and pos- 

 terior basal cusps (para- and metaconids). The second premolar differs considerably 

 from that of A. aurelianense. The anterior half of the crown is flattened on the 

 outside ; the paraconid is less enlarged and is not separated from the protoconid by 

 an external valley. This tooth appears to have neither anterior nor posterior pillars ; 

 a strong external cingulum is present on the hinder half but not on the front. The 

 third and fourth premolars do not differ in any important respect from those of the 

 European form; the anterior pillar appears to be fairly well developed, but the pos- 

 terior is reduced to very small proportions. 



The molars also resemble those of the European species ; m. 1 appears to have a 

 small anterior and a still smaller posterior pillar ; in the hinder valley is a small acces- 

 sory tubercle, but this is, no doubt, an individual variation. The second and third mo- 

 lars have no anterior pillars, the metaconid simply extending across the end of the crest 

 which runs inward from the hypoconid. This crest is not continuous with the meta- 

 conid, but is separated from it by a shallow groove. I find exactly the same condi- 

 tion of in. a and m. 3 in an almost unworn specimen of A. aurelianense from Sansan, 

 but in the large animals from Steinheim, which have been figured by Fraas (No. 12, 

 PI. VI, Fig. 2), all the molars, except m. h, have small anterior pillars, and the pos- 

 terior pillar is exceedingly reduced on m. i and absent on m. a. In A. equinum, m. a 

 has a much reduced posterior pillar and m. a a large heel. All of the lower teeth 

 from p. s to m. 3 have a strongly marked external cingulum, but none on the inner side 

 of the crown. 



The specimen does not enable us to say much with reference to the character of 



